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[Xen-API] How snapshot work on LVMoISCS SR

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Subject: [Xen-API] How snapshot work on LVMoISCS SR
From: Anthony Xu <anthony@xxxxxxxxx>
Date: Mon, 25 Jan 2010 19:43:19 -0800
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Hi all,

Basically snapshot on LVMoISCSI SR work well, it provides thin
provisioning, so it is fast and disk space efficient.

But I still have below concern.

There is one more vhd chain when creating snapshot, if I creates 16
snapshots, there are 16 vhd chains, that means when one VM accesses a
disk block, it may need to access 16 vhd lvm one by one, then get the
right block, it makes VM access disk slow. However, it is
understandable, it is part of snapshot IMO.

But after I delete all these 16 snapshots, there is still 16 vhd chains,
the disk access is still slow, which is not understandable and
reasonable, even though there may be only several KB difference between
each snapshot,

is there any way we can reduce depth of vhd chain after deleting
snapshots? get VM back to normal disk performance.

And, I notice there are useless vhd volume exist after deleting snap
shots, can we delete them automatically?

- Anthony

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