Protecting Active Directory with Snapshot Strategies

Using snapshots to protect Active Directory (AD) without careful planning will most definitely end up in a complete disaster. AD is a loosely consistent distributed multi-master database and it must not be treated as a static system.  Without carefully addressing how AD works with Time Stamps, Version Stamps, Update Sequence Numbers (USNs), Globally Unique Identification numbers (GUIDs), Relative Identification numbers (RIDs),  Security Identifiers (SIDs) and restoration requirements the system could quickly become unusable or severally damaged in the event of an incorrectly invoked snapshot reversion.

There are many negative scenarios that can occur if we were to re-introduce an AD replica to service from a snapshot instance without special handling. In the event of a snapshot based re-introduction the RID functional component is seriously impacted. In any AD system RIDs are created in range blocks and assigned for use to a participating Domain Controller (DC) by the RID master DC AD role. RIDs are used to create SIDs for all AD objects like Group or User objects and they must all be unique. Lets take a closer look at the SID to understand why RIDs are such a critical function.

A SID is composed with the following symbolic format: SRIASARID:

  • S: Indicates the type of value is a  SID.
  • R: Indicates the revision of the SID.
  • IA: Indicates the issuing authority. Most are the NT Authority identity number 5.
  • SA: Indicates the sub-authority aka domain identifier.
  • RID: Indicates the Relative ID.

Now looking at some real SID example values we see that on a DC instance only the RID component of the SID is unique as show here in red text.

DS0User1      = S1521-3725033245-1308764377-1800888333212
DS0UserGroup1 = S1521-3725033245-1308764377-1800888337611

When an older snapshot image of a DC is reintroduced it’s assigned RID range will likely have RID entries that were already used to generate SIDs. Those SIDs would have replicated to the other DCs in the AD forest. When the reintroduced DC starts up it will try to participate in replication and servicing authentications of accounts. Depending on the age and configuration of its secure channel the DC could be successfully connected. This snapshot reintroduction event should be avoided since any RID usage from the aged DC will very likely result in duplicated SID creations and is obviously very undesirable.

Under normal AD recovery methods we would either need to restore AD or build a new server and perform a DC promo on it and possibly seize DC roles if required . The most important element of an normal AD restore process is the DC GUID reinitialization function. The DC GUID value reinitialization operation  allows the restoration of an AD DC to occur correctly. A  newly generated GUID becomes part of the Domain Identifier and thus the DC can create SIDs that are unique despite the fact that the RID assignment range it holds may be from a previously used one.

When we use a snapshot image of a guest DC VM none of the required Active Directory restore requirements will occur on  system startup and thus we must manually bring the host online in DSRM mode without a network connection and then set the NTDS restore mode up. I see this as a serious security risk as there a is significant probability that the host could be brought online without these steps occurring and potentially create integrity issues.

One mitigation to this identified risk is to perform the required changes before a snapshot is captured and once the capture is complete revert the change back to the non-restore state. This action will completely prevent a snapshot image of a DC from coming online from a past time reference.

In order to achieve this level of server state and snapshot automation we would need to provision a service channel from our storage head to the involved VMs or for that matter any storage consumer. A service channel can provide other functionality beyond the NDTS state change as well. One example is the ability to flush I/O using VSS or sync etc.

We can now look at a practical example of how to implement this strategy on OpenSolaris based storage heads and W2K3 or W2K8 servers.

The first part of the process is to create the service channel on a VM or any other windows host which can support VB or Power Shell etc. In this specific case we need to provision an SSH Server daemon that will allow us to issue commands directed towards the storage consuming guest VM from the providing storage head. There are many possible products available that can provide this service. I personally like MobaSSH which I will use in this example. Since this is a Domain Controller we need to use the Pro version which supports domain based user authentication from our service channel VM.

We need to create a dedicated user that is a member of the domains BUILTINAdministrators group. This poses a security risk and thus you should mitigate it by restricting this account to only the machines it needs to service.

e.g. in AD restrict it to the DCs or possibly any involved VM’s to be managed and the Service Channel system itself.

Restricting user machine logins

A dedicated user allows us to define authentication from the storage head to the service channel VM  using a trusted ssh RSA key that is mapped to the user instance on both the VM and OpenSolaris storage host. This user will launch any execution process that is issued from the OpenSolaris storage head.

In this example I will use the name scu, which is short for Service Channel User.

First we need to create the scu user on our OpenSolaris storage head.

root@ss1:~# useradd -s /bin/bash -d /export/home/scu -P ‘ZFS File System Management’ scu
root@ss1:~# mkdir /export/home/scu
root@ss1:~# cp /etc/skel/* /export/home/scu
root@ss1:~# echo PATH=/bin:/sbin:/usr/ucb:/etc:. > /export/home/scu/.profile
root@ss1:~# echo export PATH >> /export/home/scu/.profile
root@ss1:~# echo PS1=$’${LOGNAME}@$(/usr/bin/hostname)’~#’ ‘ >> /export/home/scu/.profile

root@ss1:~# chown –R scu /export/home/scu
root@ss1:~# passwd scu

In order to use an RSA key for authentication we must first generate an RSA private/public key pair on the storage head. This is performed using ssh-keygen while logged in as the scu user. You must set the passphrase as blank otherwise the session will prompt for it.

root@ss1:~# su – scu

scu@ss1~#ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/export/home/scu/.ssh/id_rsa):
Created directory ‘/export/home/scu/.ssh’.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /export/home/scu/.ssh/id_rsa.
Your public key has been saved in /export/home/scu/.ssh/
The key fingerprint is:
0c:82:88:fa:46:c7:a2:6c:e2:28:5e:13:0f:a2:38:7f scu@ss1

We now have the public key available in the file named the content of this file must be copied to the target ssh instance file named .ssh/authorized_keys. The private key file named id_rsa MUST NOT be exposed to any other location and should be secured. You do not need to store the private key anywhere else as you can regenerate the pair anytime if required.

Before we can continue we must install and configure the target Service Channel VM with MobaSSH.

Its a simple setup, just download MobaSSH Pro to the target local file system.

Execute it.

Click install.

Configure only the scu domain based user and clear all others from accessing the host.


Moba Domain Users

Once MobaSSH is installed and restarted we can connect to it and finalize the secured ssh session. Don’t forget to add the scu user to your AD domains BUILTINAdministrators group before proceeding.  Also you need to perform an initial NT login to the Service Channel Windows VM using the scu user account prior to using the SSH daemon, this is required to create it’s home directories.

In this step we are using  putty to establish an ssh session to the Service Channel VM and then secure shelling to the storage server named ss1. Then we transfer the public key back to our self using scp and exit host ss1. Finally we use cat to append the public key file content to our  .ssh/authorized_key file in the scu users profile. Once these steps are complete we can establish an automated prompt less secured encrypted session from ss1 to the Service Channel Windows NT VM.

[Fri Dec 18 – 19:47:24] ~
[scu.ws0] $ ssh ss1
The authenticity of host ‘ss1 (’ can’t be established.
RSA key fingerprint is 5a:64:ea:d4:fd:e5:b6:bf:43:0f:15:eb:66:99:63:6b.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added ‘ss1,’ (RSA) to the list of known hosts.
Last login: Fri Dec 18 19:47:28 2009 from
Sun Microsystems Inc.   SunOS 5.11      snv_128 November 2008

scu@ss1~#scp .ssh/ ws0:/home/scu/.ssh/
scu@ws0’s password:           100% |*****************************|   217       00:00

[Fri Dec 18 – 19:48:09]
[scu.ws0] $ cat .ssh/ >> .ssh/authorized_keys

With our automated RSA key password definition completed we can proceed to customize the MobaSSH service instance to run as the scu user. We need to perform this modification in order to enable VB script WMI DCOM impersonate caller rights when instantiating objects. In this case we are calling a remote regedit object over WMI and modifying the NTDS service registry start up values and thus this can only be performed by an administrator account. This modification essentially extends the storage hosts capabilities to reach any Windows host that need integral system management function calls.

On our OpenSolaris Storage head we need to invoke a script which will remotely change the NTDS service state and then locally snapshot the provisioned storage  and lastly return the NTDS service back to a normal state.  To accomplish this function we will define a cron job. The cron job needs some basic configuration steps as follows.

The is required to submit a cron job, this allows us to create the job but not administer the cron service.
If an /etc/cron.d/cron.allow file exists then this RBAC setting will be overridden by the files existence and you will need to add the user to that file or convert to the best practice methods of RBAC.

root@ss1~# usermod -A scu
root@ss1~# crontab –e scu
59 23 * * * ./

Hint: crontab uses vi –  “vi cheat sheet”

The key sequence would be hit “i” and key in the line then hit “esc :wq” and to abort “esc :q!”

Be aware of the timezone the cron service runs under, you should check it and adjust it if required. Here is a example of whats required to set it.

root@ss1~# pargs -e `pgrep -f /usr/sbin/cron`

8550:   /usr/sbin/cron
envp[0]: LOGNAME=root
envp[1]: _=/usr/sbin/cron
envp[2]: LANG=en_US.UTF-8
envp[3]: PATH=/usr/sbin:/usr/bin
envp[4]: PWD=/root
envp[5]: SMF_FMRI=svc:/system/cron:default
envp[6]: SMF_METHOD=start
envp[7]: SMF_RESTARTER=svc:/system/svc/restarter:default
envp[8]: SMF_ZONENAME=global
envp[9]: TZ=PST8PDT

Let’s change it to CST6CDT

root@ss1~# svccfg -s system/cron:default setenv TZ CST6DST

Also the default environment path for cron may cause some script “command not found” issues, check for a path and adjust it if required.

root@ss1~# cat /etc/default/cron
# Copyright 1991 Sun Microsystems, Inc.  All rights reserved.
# Use is subject to license terms.
#pragma ident   “%Z%%M% %I%     %E% SMI”

This one has no default path, add the path using echo.

root@ss1~# echo PATH=/usr/bin:/usr/sbin:/usr/ucb:/etc:. > /etc/default/cron
# svcadm refresh cron
# svcadm restart cron

With a cron job defined to run the script named in the default home directory of the scu user we are now ready to create the script content. Our OpenSolaris storage host needs to call a batch file on the remote Service Channel VM and it will execute  a vbscript from there to set the NTDS start up mode . To do this from a unix bash script we will use the following statements in the file.

ssh -t ws0 NTDS-PreSnapshot.bat
snap_date=”$(date +%d-%m-%y-%H:%M)”
pfexec zfs snapshot rp1/san/vol1@$snap_date
ssh -t ws0 NTDS-PostSnapshot.bat

Here we are running a secure shell call to the MobaSSH daemon with a -t option which runs the tty screen locally and this allows use to issue an “exit” from the remote calling script closing the secure shell. On the Service Channel VM the followng batch file vbscript calls are executed using the pre and post batch files illustrated as follows.

scu Batch Files

cscript NTDS-SnapshotRestoreModeOn.vbs DS0

cscript NTDS-SnapshotRestoreModeOff.vbs DS0


strComputer = Wscript.Arguments(0)  
const HKLM=&H80000002
Set oregService=GetObject(“WinMgmts:{impersonationLevel=impersonate}!\” & strComputer & “rootdefault:stdRegProv”)
oregService.SetDWordValue HKLM, “SYSTEMCurrentControlSetServicesntdsparameters”, “Database restored from   backup”, 1
Set oregService=Nothing


strComputer = Wscript.Arguments(0)  
const HKLM=&H80000002
Set oregService=GetObject(“WinMgmts:{impersonationLevel=impersonate}!\” & strComputer & “rootdefault:stdRegProv”)
oregService.SetDWordValue HKLM, “SYSTEMCurrentControlSetServicesntdsparameters”, “Database restored from   backup”, 0
Set oregService=Nothing

We now have Windows integrated storage volume snapshot functionality that allows an Active Directory domain controller to be securely protected using a snapshot strategy. In the event we need to fail back to a previous point in time there will be no danger that the snapshot will cause AD corruption. The integration process has other highly desirable capabilities such as the ability to call VSS snapshots and any other application backup preparatory function calls.  We could also branch out using more sophisticated PowerShell calls to VMware hosts in a fully automated recovery strategy using ZFS replication and remote sites.

Hope you enjoyed this entry.

Seasons Greetings to All.



Site Contents: © 2009  Mike La Spina

Controlling Snapshot Noise

The ability to perform file system, database and volume snapshots grants us many data protection benefits. However there are some serious problems that can occur if we do not carefully architect snapshot based storage infrastructures. This blog entry will discuss some of the issues with data noise induction and data integrity when using point in time data snapshot activities  and how we can reduce the negative aspects of these data protection methods.

With the emergence of snapshot technology in the data center data noise induction is an unwanted by product and needs to addressed. Active data within a file store or raw volume will have significant amounts of temporary data like  memory swaps and application temp files. This type of data is required for system operations but unfortunately it is completely useless within a point in time snapshot and simply consumes valuable storage space with no permanent value within the scope of system data protection. There are many sources of this undesirable data noise that we need to consider and define strategies to isolate and eliminate them where possible.

In some cases using raw stores eg. iSCSI, FC etc. we will have duplicate snapshot functionality points in the storage stream and this further complicates how we approach a solution to noise induction issues. One common example of snapshot functionality duplication is Microsoft Windows 2003 Volume Snapshot Service aka. VSS. If we enable VSS and an external snapshot service is employed then we are now provisioning snapshots of snapshots which of course is less than optimal because much of the delta between points in time are just redundant encapsulated data. There are some higher level advantages to allowing this to occur like provisioning self service end user restores and VSS aware file system quiescence but for the most part it is not optimal from a space consumption or performance and efficiency  perspective.

If we perform snapshots at multiple points in the data storage stream using VSS we will have three points of data delta. The changed data elements on the source store of the primary files, a copy-on-write set of  changed blocks of the same primary store including it’s meta data and finally the external snapshot delta and it’s meta data. As well if the two snapshot events were to occur at the same time it creates a non-integral copy of a snapshot and meta data which is just pure wasted space since it is inconsistent.

With the co-existing use of VSS we need to define what functionality is important to us. For example VSS is limited to 512 snapshots and 64 versions so if we need to exceed these limits we have to employ an external snapshot facility. Or perhaps we need to allow a user self service file restore functionality from a shared folder. In many cases this functionality is provided by the external snapshot provisioning point. OpenSolaris, EMC and NetApp are some examples of storage products that can provide such functionality. Of course my preference is Custom OpenSolaris storage servers or the S7000 series of storage product which is based on OpenSolaris and is well suited for the formally supported side of things.

Solely provisioning the snapshots externally verses native MS VSS can significantly reduce induced data noise if the external provider supports VSS features or provides tools to control VSS. VSS copy on write snapshot capability should not be active when using this strategy so as to eliminate the undesirable snapshot echo noise. Most environments will find that they require the use of snapshot services that exceed the native MS VSS capabilities.  Provisioning the snapshot function directly on a shared storage system is a significantly better strategy verses allowing a distributed deployment of storage management points across your infrastructure.

OpenSolaris and ZFS provides superior depth in snapshot provisioning than Microsoft shared folder snapshot copy services. Implementing ZFS dramatically reduces space consumption and allows snapshots up to the maximum capacity of the storage system and OpenSolaris provides MS SMB client access to the snapshots which users can manage recovery as a self service. By employing ZFS as a backing store, snapshot management is simplified and snapshots are  available for export to alternate share points by cloning and provisioning the point in time to data consumers performing a multitude of desirable tasks such as audits, validation, analysis and testing.

If we need to employ MS VSS snapshot services provisioned on a storage server that uses snapshot based data protection strategies  then we will need prevent  continuous snapshots on the storage server. We can use features like snap mirror and zfs replication to provision a replica of the data however this would need to be strictly limited in count e.g. 2 or 3 versions and timed to avoid a multiple system snapshot time collision. Older snapshots should be purged and we only allow the MS VSS snapshot provisioning to keep the data deltas.

Another common source of snapshot noise is temporary file data or memory swaps. Fortunately with this type of noise the solution is relatively easy to solve as we simply isolate this type of storage onto storage volumes or shares that are explicitly excluded from a snapshot service function. For example if we are using VMFS stores we can place vswp files on a designated VMFS volume and conversely within an operating system we can create a separate vmdk disk that maps to a VMFS volume which we also exclude from the snapshot function. This strategy requires that we ensure that any replication scheme incorporates the creation or one time replication of these volumes. Unfortunately this methodology does not play well with storage vmotion so one must ensure that the a relocation does not move the noisy vmdk’s back into the snapshot service provisioned stores.

VMware VMFS volume VM snapshots is a significant source of data noise. When a snapshot is initiated from within VMware all data writes are placed on delta file instances. These delta files will be captured on the external storage systems snapshot points and will remain there after the VM snapshot is removed. Significant amount of data delta are produced by VM based snapshots and sometimes mulitple deltas can exceed original vmdk size. An easy way to prevent this undesirable impact is to clone the VM to a store outside the snapshot provisioned stores rather than invoking snapshots.

Databases are probably the most challenging source of snapshot noise data and requires a different strategy than isolation because the data within a specific snapshot is all required to provide system integrity. For example we cannot isolate SQL log data because it is required to do a crash recovery or to roll forward etc.  We can isolate temp database stores since any data in those date stores would not be valid in a crash recovery state.

One strategy that I use as both a blanket method when we are not are able to use other methods and in concert with the previously discussed isolation methods is a snapshot roll-up function. This strategy simply reduces the number of long term snapshot copies that are kept. The format is based on a Grand Father, Father and Son (GFS) retention chain of the snapshot copies and is well suited for a variety of data types. The effect is to provide a reasonable amount of data protection points to satisfy most computing environments and keep the captured noise to a manageable value. For example if we were to snapshot without any management cycle every 15 minutes we would accumulate ~35,000 delta points of data over the period of 1 year. Conversely if we employ the GFS method we will accumulate 294 delta points of data over the period of 1 year. Obviously the consumption of storage resource is so greatly reduced that  we could keep many additional key points in time if we wished and still maintain a balance of recovery point verses consumption rate.

Let’s take a look at a simple real example of how snapshot noise can impact our storage system using VMware, OpenSolaris and ZFS block based iSCSI volume snapshots. In this example we have a simple Windows Vista VM that is sitting idle, in other words only the OS is loaded and it is power on and running.

First we take a ZFS snapshot of the VMFS ZFS iSCSI volume.

zfs snapshot sp1/ss1-vol0@beforevmsnap

Now we invoke a VMware based snapshot and have a look at the result.

root@ss1:~# zfs list -t snapshot
NAME                               USED  AVAIL  REFER  MOUNTPOINT
sp1/ss1-vol0@beforevmsnap          228M      –  79.4G  –

Keep in mind that we are not modifying any data files in this VM if we were to change data files the deltas would be much larger and in many cases with multiple VMware snapshots could exceed the VMs original size if it is allowed to remain for long periods of weeks and longer. The backing store snapshot initially consumes 228MB which will continue to grow as changes occurs on the volume. A significant part of the 228MB is the VMs memory image in this case and of course it has no permanent storage value.

sp1/ss1-vol0@after1stvmsnap          1.44M      –  79.5G  –

After the initial VMware snapshot occurs we create a new point in time ZFS snapshot and here we observe some noise in the next snapshot and again we have not changed any data files in the last minute or so.

sp1/ss1-vol0@after2ndvmsnap       1.78M      –  79.5G  –

And yet another ZFS snapshot a couple of minutes later shows more snapshot noise accumulation. This is one of the many issues that are present when we allow non-discretionary placement of files and temporary storage on snapshot based systems.

Now lets see the impact of destroying a snapshot that was created after we delete the VMware based snapshot.

root@ss1:~# zfs destroy sp1/ss1-vol0@beforevmsnap
root@ss1:~# zfs list -t snapshot
NAME                               USED  AVAIL  REFER  MOUNTPOINT
sp1/ss1-vol0@after1stvmsnap       19.6M      –  79.2G  –
sp1/ss1-vol0@after2ndvmsnap       1.78M      –  79.2G  –

Here we observe the reclamation of more than 200MB of storage. And this is why GFS based snapshot rollups can provide some level of noise control.

Well I hope you found this entry to be useful.

Til next time..




Site Contents: © 2009  Mike La Spina

iSCSI Security Basics

With iSCSI’s growing popularity the need for improved iSCSI security understanding is becoming very important. Multiple issues arise when we choose to transport storage over our networks. The fundamental security areas of availability, confidentiality and integrity are all at risk when iSCSI best practices are not implemented. For example a single attachment error can corrupt an iSCSI attached device at the speed of electrons. An entire data volume can be connected to an unauthorized users system. Access can be interrupted by a simple network problem. The possible outage issues are many and far reaching thus we must carefully assess our risk and mitigate them where appropriate.

The most important step to a best practice is good old planning. It never fails to amaze me when I see instances of adhoc implementations of highly sensitive storage system architectures. Without fail the adhoc unplanned method will result in unstable systems. Primarily due to forced system changes that were required to correct a multitude of issues like miss-configuration, poor performance, miss matched firmware etc. Planning is one of the most difficult parts of the process where we almost need to be a fortune teller. You have to ask yourself the proverbial 1000 questions and come up with the right answers. So where do you begin? Well a good start would be to use a risk based approach. How much would it cost if a failure occurred and what data is most critical, how much is the data worth etc. We need to walk through the possible events and determine what make sense to prevent the events and when not to overdo it.

Some of the more obvious ways to prevent security events are to build on fundamental best practices like the following.


  • Build a physically separate network to service iSCSI
  • Zone the services with VLANS
  • Provide power redundancy to all devices (Separate UPS etc.)  
  • Provide a minimum of two data paths to all critical components
  • Disable unused ports
  • Physically secure all the iSCSI network access points
  • Use mutual authentication
  • Where appropriate use TOE (TCP Offloading Engine) hardware but be careful of complexity
  • Encrypt data crossing a WAN      

The physical separation of the iSCSI network domain is important in many ways. We can prevent unpredictable capacity demands and provide much greater security by reducing the unauthorized physical connectivity. Change control is simplified and can be isolated. External network undesirables are completely eliminated. The dedicated physical network segregation practice is probably the single most important step of building a stable secure iSCSI environment.

Just as we segregate zones on traditional FCP based SAN’s the same practice is beneficial in the iSCSI world, we can filter and control OS based access and data flow we can isolate authentication and name services, performance monitoring can be observed in a VLAN context. Priority can be controlled on a per VLAN context.

I can never forget the day one of our circuit breakers popped in the DC, alarms were TAPped out and a feeling of panic stirred. But that’s when planning pays off. The system continued to run on the secondary power line. So by simply powering on a server you can pop a weak breaker and kill the entire system. So when it comes to power supplies, I take them very seriously. Use TRUE power redundancy on all devices that are part of a critical SAN system, iSCSI or not. It will likely save your bacon in a multitude of scenarios.

No matter how hard we try to be perfect, it is in our nature to make mistakes. And when you are staring at a bundle of cables they really do all look the same. Moving the wrong cable or a port failure can completely take out your iSCSI functionality. Worse yet, a switch module dies on you. For the cost of  a an additional port we can avoid all of these ugly scenarios, besides multi pathing gives you more peek bandwidth. And you gain the ability to do firmware updates without a full outage. Data path redundancy is a must for critical systems.

My neighbor had an interesting story the other day. He kept popping breakers when only two car block heaters were in use. (Block Heater? Yes up north when its cold you have to keep your cars plugged in. And no, we don’t live in igloos) So what does this have to do with iSCSI. Well my neighbor has discovered that if you have a power receptacle available other people will use it. They didn’t ask to use it and he did not expect them to, but you get the point. Your IT neighbors will at some point do the same so disable accessible ports by default and enable only what is in supposed to be in use. 

If my neighbor could have locked the receptacle he would not need to worry about disabling it, but security is about layers of prevention. The more you have the less likely that a breach will happen and preventing physical access is usually easy.

The fastest way to corrupt an iSCSI target is to allow unauthenticated access. It’s just to easy to connect to the wrong node. I decided to do a quick test the other day which involved connecting two Windows initiators to a target. On one I created a directory with jpg photos and on the other I connected and browsed to the photo directory. Bam corrupt target! The second node wrote a thumb nail while the first node copied more photos to the target. Its just completely crazy to run without authentication and one way authentication is not going to prevent this in many cases. Thus we should use a mutual authentication and no it does not make it less hackable but it does help prevent the more probable human error event. For example most IT shops will not want to have separate passwords for every iSCSI CHAP Pair, they will likely use one for many nodes to reduce the administrative overhead. Using the same passwords essentially allows the connection of any correctly configured initiator to any correctly configured target. If you couple a single password config with mutual authentication then you must define the return target access on the respective initiator and this reduces accidental connections to the wrong node. A small amount of effort will prevent this human error and it costs nothing to setup. Of course you can have unique passwords on every iSCSI host, it will however require a central password store and far more administration in larger configurations. There are other solutions but those are out of scope for this basic security blog.

If you anticipate heavy traffic or plan to use IPSec you will want to consider TCP Offload Engine Adaptors (TOE). This does not mean that every server should use TOE on the contrary you should evaluate the iSCSI network traffic of the service and the server CPU utilization level on that server. You can anticipate that 1Gb of sustained iSCSI network will consume about 25% of a 3 Ghz Dual CPU server for strait iSCSI work. IPSec will vary depending on the key size and the OS implementation of the IPSec protocol so I can’t even ball park it. An example where it would make a lot of sense to use a TOE is in the case of a VMware ESX host where you want as much CPU as possible available to VM’s. The TOE Adaptor will do all the iSCSI and IPSec work and the server CPU is all left to the VM’s. It does not make sense if the host will be underutilized and a medium amount of network traffic is predictable. You will also want to consider keeping your IPSec implementation as simple as possible. When a problem occurs, things can get very difficult to analyze and correct with IPSec as well setting up IPSec can be painful if things do not go as planned. (Blog on that subject to come later)

This PDF link provides some excelent information on IPSec and iSCSI performance.  

If you have a DR centre or other multisite iSCSI functions across a WAN you will need to consider if data encryption is required. For example if you are using an external network provider then you should definitely be encrypting the data. If securing the data is not critical then consider using compression of some type at the bare minimum. You will promote better availability and as an added bonus the data is will not cross the WAN in the clear for your neighbors to view. If encryption is important then IPSec is a good solid inexpensive way of ensuring confidentiality, integrity and authenticationt. There are many options available to secure the transmission over the WAN. It should be easy to manage and conform to industry standards like 128Bit AES symmetric ciphers which are reasonably fast and extremely secure when managed correctly.

Till Next Time



Site Contents: © 2008  Mike La Spina