thin provisioning

[cblakely]

Hi folks -

I've got a proof of concept environment running on 5.1SP1PR2 on RHEL6. Our backend storage is equalogic arrays via iscsi. I am interested in thin provisioning at the vxvm/vxfs level (similar to multiple volumes of any arbitrary size in the same zfs pool on solaris). Is this possible, or is the only support for thin disks in storage foundation to use a thin lun with the thin reclamation feature (of which our arrays are not compatible with, per the HCL).

In my mind they are two different features - thin provisioning only alloocates space from the on first use. Thin reclamation would return space to the array as blocks are freed by the filesystem. Obviously both together is the desired end state, but even if I can't reclaim space, I'd like to at least not allocate it until it needs to be.

Thanks,

CB

[mikebounds · Accepted solution]

VxVM and in fact any logical volume Management supports thin LUNs from any array - i.e. space is only allocated when it is used by the filesystem.  Looking at the latest HCL (http://www.symantec.com/business/support/index?page=content&id=TECH74012), none of the iSCSI EqualLogic arrays support Thin reclamation.

Another important feature of thin provisioning is when using mirroring.  Usually when you create a mirror of a volume, it is mirrored at block level so any unused space in the filesystem will be written on the mirror so the mirror is not thin provisioned.  With VxVM (for any array) you can smart mirror so that only blocks that are used are written.  This is essential for migrating from non-thin to thin and just for any mirroring in general.

Mike