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October, 2008

Read/Write iSCSI Snapshots on a Celerra

If you notice the dates on my posts you’ll see I haven’t been blogging lately but that doesn’t mean I’m not working on some interesting things.  Lately I’ve been doing a lot with snapshots from iSCSI LUNs on Celerras while playing with VMware’s VDM.  The Celerra CLI allows you to do some powerful things with scripting and snapshots.  I’ll have a post soon showing some PowerShell scripts and VDI, but in the mean time….

The first step to creating a snapshot is to list the available iSCSI LUNs on the Celerra.

[[email protected] ~]$ server_iscsi ALL -lun -list
server_2 :
lun        size(MB)        filesystem
0          245000          VI3LAB_ISCSI_VMFS ( id=49 )
5          19500           VDI_Demo ( id=55 )

lun        size(MB)        filesystem
1          49000           VCLAB_ISCSI ( id=54 )

As you can see we have a few LUNs available.  For this demonstration we’ll be using LUN 5 on iSCSI target VI3_ISCSI_TARGET.  The next step is to create a snapshot from LUN 5.

[[email protected] ~]$ server_iscsi ALL -snap -create -target VI3_ISCSI_TARGET -lun 5
Info 26306936878:

Note the name of the snapshot, fs55_T2_LUN5_APM00080902485_0000.ckpt452.  You can display information about a snapshot.

[[email protected] ~]$ server_iscsi ALL -snap -info fs55_T2_LUN5_APM00080902485_0000.ckpt452
Snap Name = fs55_T2_LUN5_APM00080902485_0000.ckpt452
Lun Number = 5
Promoted Number = 128
Promoted Initiator =
Application Label = CelerraCS
LUN Size MB = 19500
Create Time = Wed Oct 29 09:16:47 GMT+05:00 2008
Application Data =

Now that you have created the snapshot you can promote it to Read/Write status, connect it to an iSCSI target, and assign any iSCSI initiators for access.

[[email protected] ~]$ server_iscsi ALL -snap -promote fs55_T2_LUN5_APM00080902485_0000.ckpt452 -initiator

Notice that you didn’t designate a LUN number. By default it will start assigning LUNs at 128.

[[email protected] ~]$ server_iscsi ALL -lun -list
server_2 :
lun size(MB) filesystem
0 245000 VI3LAB_ISCSI_VMFS ( id=49 )
5 19500 VDI_Demo ( id=55 )
128 19500 VDI_Demo ( id=55 )

lun size(MB) filesystem
1 49000 VCLAB_ISCSI ( id=54 )

At this point you can mount the LUN from an iSCSI client and use it just like you can the original LUN. Once you are finished with that LUN you can demote it.

[[email protected] ~]$ server_iscsi ALL -snap -Demote APM00080902485_0000.ckpt452

The key here is that you can easily create a lot of snapshots and Read/Write mountable iSCSI LUNs using scripts and put these to use.  These are also useful for testing and recovery.  Snap a LUN with a database on it, mount it on another system, and then do an upgrade test against the production data without touching the production server.

47 thoughts on “Read/Write iSCSI Snapshots on a Celerra”

  1. Hi Jason. Grreat post, I was just about to start playing with this in the Lab when I come across your post.


  2. Jason

    Greate post. I followed your doucment step by step and it worked great. I am able to craete , promote , Demote the iSCSI snap to local / remote server.

    Can you mail me once you post the powerful script to do the same iSCSI snap using CLI (Script)


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