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Fred2010's avatar
Fred2010
Level 6
14 years ago

SCSI-3 or not to SCSI-3 ?!?

Hi, I am about to setup a new 3 node cluster, using Storage Foundation for Windows HA (SFW HA version 5.1 SP2 downloaded). This Cluster is going to be a 3 Node Netbackup Masterserver (NBU 7.1 FA)...
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Storage Foundation for Windows
  • rhanley's avatar
    rhanley
    14 years ago

    Hi Fredster,

        I should be able to answer your questions here:

    First off, your array: EMC Clariion CX3-80 (Flare 26 subversion 025)

    You can check compatability from our 5.1 SP2 HCL which can be found here: http://www.symantec.com/docs/TECH138719

    In the case of using this with PowerPath 5.5.0, this has not been tested, but this should work as stated in the HCL notes:

    Note 1: The 3rd party multi-pathing support noted for this array or array family should be compatible, but has not been explicitly tested by Symantec with this particular array or array family at this time.

    The 2nd note for (Note 5) also shows that support includeds the CX3-80 Array:

    EMC CLARiiON CX Series arrays supported include the CX200, CX300, CX400, CX500, CX600 and CX700. EMC CLARiiON CX-3 Ultrascale Series arrays supported include the CX3-10, CX3-20, CX3-40 and CX3-80 arrays. EMC CLARiiON AX Series arrays supported include the AX100, AX150, AX4.

    I have reached out to the team responsible for this testing requesting additional information (confirm that 5.5 is supported and if there are any plans to test this in the future). I will reply to this thread as soon as I have that detail.

    1) Can I use SCSI-3 Persistent Group Reservervations in this setup?

    Yes you can, as long as your array is configured to support this (which it should as you stated). You can use a utility we have (scsicmd) to run a SCSI3 Test to make certain this works properly before making the change. More information on this utility can be found here: http://www.symantec.com/business/support/index?page=content&id=TECH72086

    Note: The SCSI3_Test command and example are the very last example shown in this technote. At the beginning of this technote is a url where the scsicmd utility can be downloaded (ftp.veritas.com/pub/support/vmtools - Filename: scsicmd.zip).

    When running the command, just choose any of the harddisks from the array to perform the test on (you do not need to test each lun, just one from each array).

    2) What is the advantage for me to use SCSI-3 PGR instead of using SCSI-2 (Which seems to be the default).

    SCSI-3 is preferred because of the way it handles reserving/releasing reservations is more efficient than SCSI-2 so there may be slight performance increases from using SCSI-3 over SCSI-2. This is very minimal and in most configurations, changing between SCSI-2 and SCSI-3 would not be noticeable and both would function properly.

    However, SCSI-3 is required in a cluster if Active/Active multipathing is being used. With Clariion arrays, you can use Active/Passive Concurrent which supports SCSI-2, but if you are using ALUA, then you will need to use SCSI-3.

    3) Are there any disadvantages/Gotcha's in using SCSI-3 angry

    As stated, SCSI-3 is more efficient in multipathing as all paths share the same reservation key. In an Active/Active multipathing configuration, all paths share the same reservation key so there is no checking, release, renewing reservations with path failovers. With SCSI-2, a reservation is path specfic so after sending I/O down Path1, Path 2 will check for a reservation, release it if one exists, then send a new reservation request, then send the I/O. Though these processes take miliseconds to complete, in large, I/O intesive environments, there may be performance improvement seen by moving from SCSI-2 to SCSI-3.

    If your array passes the scsi3_test with the scsicmd utility, then I'd strongly advice using SCSI-3 for the reasons explained above and the fact that all arrays are moving to this (in fact, Windows Failover Cluster in 2008 already requires SCSI-3) and in the future, SCSI-2 will be phased out completely.

    On a final note, when switching from SCSI-2 to SCSI-3, you will want to perform the following steps:

    1. Take all cluster groups containing VMDg resources offline (or move them to another node in the cluster). If the Quorum is Dynamic (VMDg resource), move this to another node in the cluster.

    2. Change from SCSI-2 to SCSI-3 from the VEA console (Control Panel > Storage Agent > System Settings > SCSI Support > SCSI-3 support)

    3. From a command prompt, restart the Veritas Storage Agent by running the following 2 commands:
        - net stop vxvm
        - net start vxvm

    4. Bring the cluster groups containing VMDg resources back online, or move them back to this node if they were failed over in Step 1.

    5. You can then use the scsicmd scsi_reserved_status command to view/confirm the disks are reserved under SCSI-3.
     

    Please let me know if you have any additional questions, and I'll also update the post as soon as I've heard back on my queries concerning support for PowerPath 5.5.0.

    Cheers,
    rhanley

rhanley's avatar
rhanley
Level 4
14 years ago

Hi Fredster,

    I should be able to answer your questions here:

First off, your array: EMC Clariion CX3-80 (Flare 26 subversion 025)

You can check compatability from our 5.1 SP2 HCL which can be found here: http://www.symantec.com/docs/TECH138719

In the case of using this with PowerPath 5.5.0, this has not been tested, but this should work as stated in the HCL notes:

Note 1: The 3rd party multi-pathing support noted for this array or array family should be compatible, but has not been explicitly tested by Symantec with this particular array or array family at this time.

The 2nd note for (Note 5) also shows that support includeds the CX3-80 Array:

EMC CLARiiON CX Series arrays supported include the CX200, CX300, CX400, CX500, CX600 and CX700. EMC CLARiiON CX-3 Ultrascale Series arrays supported include the CX3-10, CX3-20, CX3-40 and CX3-80 arrays. EMC CLARiiON AX Series arrays supported include the AX100, AX150, AX4.

I have reached out to the team responsible for this testing requesting additional information (confirm that 5.5 is supported and if there are any plans to test this in the future). I will reply to this thread as soon as I have that detail.

1) Can I use SCSI-3 Persistent Group Reservervations in this setup?

Yes you can, as long as your array is configured to support this (which it should as you stated). You can use a utility we have (scsicmd) to run a SCSI3 Test to make certain this works properly before making the change. More information on this utility can be found here: http://www.symantec.com/business/support/index?page=content&id=TECH72086

Note: The SCSI3_Test command and example are the very last example shown in this technote. At the beginning of this technote is a url where the scsicmd utility can be downloaded (ftp.veritas.com/pub/support/vmtools - Filename: scsicmd.zip).

When running the command, just choose any of the harddisks from the array to perform the test on (you do not need to test each lun, just one from each array).

2) What is the advantage for me to use SCSI-3 PGR instead of using SCSI-2 (Which seems to be the default).

SCSI-3 is preferred because of the way it handles reserving/releasing reservations is more efficient than SCSI-2 so there may be slight performance increases from using SCSI-3 over SCSI-2. This is very minimal and in most configurations, changing between SCSI-2 and SCSI-3 would not be noticeable and both would function properly.

However, SCSI-3 is required in a cluster if Active/Active multipathing is being used. With Clariion arrays, you can use Active/Passive Concurrent which supports SCSI-2, but if you are using ALUA, then you will need to use SCSI-3.

3) Are there any disadvantages/Gotcha's in using SCSI-3 angry

As stated, SCSI-3 is more efficient in multipathing as all paths share the same reservation key. In an Active/Active multipathing configuration, all paths share the same reservation key so there is no checking, release, renewing reservations with path failovers. With SCSI-2, a reservation is path specfic so after sending I/O down Path1, Path 2 will check for a reservation, release it if one exists, then send a new reservation request, then send the I/O. Though these processes take miliseconds to complete, in large, I/O intesive environments, there may be performance improvement seen by moving from SCSI-2 to SCSI-3.

If your array passes the scsi3_test with the scsicmd utility, then I'd strongly advice using SCSI-3 for the reasons explained above and the fact that all arrays are moving to this (in fact, Windows Failover Cluster in 2008 already requires SCSI-3) and in the future, SCSI-2 will be phased out completely.

On a final note, when switching from SCSI-2 to SCSI-3, you will want to perform the following steps:

1. Take all cluster groups containing VMDg resources offline (or move them to another node in the cluster). If the Quorum is Dynamic (VMDg resource), move this to another node in the cluster.

2. Change from SCSI-2 to SCSI-3 from the VEA console (Control Panel > Storage Agent > System Settings > SCSI Support > SCSI-3 support)

3. From a command prompt, restart the Veritas Storage Agent by running the following 2 commands:
    - net stop vxvm
    - net start vxvm

4. Bring the cluster groups containing VMDg resources back online, or move them back to this node if they were failed over in Step 1.

5. You can then use the scsicmd scsi_reserved_status command to view/confirm the disks are reserved under SCSI-3.
 

Please let me know if you have any additional questions, and I'll also update the post as soon as I've heard back on my queries concerning support for PowerPath 5.5.0.

Cheers,
rhanley