Spring Switzerland GmbH Ver. 1.61 manual Using snapshot with Open-E iSCSI

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Using snapshot with Open-E iSCSI

Usage snapshot facility heavily depends on the initiator of software support for dynamic units* and the partition scheme which you use on the operating system where you attach the targets. The most common error is if on the client side that uses an LVM/LVM2 (Linux) scheme or Microsoft's Dynamic Disks which connect to the snapshot and original volume from the same client malfunctions. This is due to the fact that normally an LVM volume bares special metadata which is used as the identify information and since a snapshot simply doubles those metadata it can confuse your partitioning software (for example logical volume manager sees two identical volumes).

In order to take proper advantage of Open-E iSCSI Target's snapshot technology the volumes your Open-E iSCSI Target exports should be imported in your operating system as Basic Volume (Windows) and you should not incorporate them as logical volumes in LVM/LVM2 (on Linux) if you plan to use snapshots and access them from the same machine at the same time.

If you plan to take snapshots and import them alongside the original volume - access them from the same client. Below is instruction how to import a target in a Microsoft basic volume:

a.Create target volumes (tgv),

b.Create a target in Open-E iSCSI,

c.Add chosen volumes to the target.

d.In MS iSCSI Initiator add Open-E iSCSI Target as an iSCSI portal in the MS iSCSI Initiator console,

e.Log onto the target,

f.Open the computer management,

g.Select the disk management,

h.Add the volumes as basic disks,

i.On Open-E iSCSI Target create snapshots: setup Æ target manager and reserve desired space for snapshots (reserve about 5-20% of total space for the snapshots). Determine number of snapshots, assigned to the volumes and distribute the reserved space as needed. To activate a snapshot go Maintenance Æ Snapshot.

j.Follow the steps e-h to log and attach the snapshot target.

*) Currently iSCSI Microsoft Initiator ver1.06 does not support dynamic volumes.

The best solution to use snapshots without decreasing Open-E iSCSI performance is to assign separate RAID. This RAID will be optimized for a writing speed (e.g. few disks in RAID 0 only for snapshots). Follow the steps below:

a.Add RAID chosen for data as NEW (Vg0) in the menu WebGui: setup Æ target manager Æ Volumes,

b.Create one or more Tgv’s. At this point, there is no free space reserved for snapshots,

c.Add the second RAID to existing Vg0, intended for snapshots, (RAID previously configured as RAID 0),

d.Now only reserve all available space for snapshots.