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RE: [Xen-API] How snapshot work on LVMoISCS SR

To: 'Anthony Xu' <anthony@xxxxxxxxx>, "xen-api@xxxxxxxxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-API] How snapshot work on LVMoISCS SR
From: Dave Scott <Dave.Scott@xxxxxxxxxxxxx>
Date: Tue, 26 Jan 2010 10:48:37 +0000
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Hi Anthony,

> 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,

There is a background "coalesce" and "GC" process which will delete 14 of these 
16 vhds in the background, provided you haven't called "clone" on any of them: 
the nodes can only be deleted if they are unused.

> 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?

The "GC" process will delete exactly those volumes which are unused, acquiring 
the appropriate locks. Don't delete them yourself or something bad might happen!

Unfortunately there's no current way to monitor the progress of the "coalesce" 
and "GC" :( This is something we hope to improve in the future.


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