From: Joe Pruett <joey@q7.com>
To: LVM general discussion and development <linux-lvm@redhat.com>
Subject: Re: [linux-lvm] advice for curing terrible snapshot performance?
Date: Mon, 15 Nov 2010 10:08:11 -0800 [thread overview]
Message-ID: <4CE1770B.8000007@q7.com> (raw)
In-Reply-To: <AANLkTimzHm_zhG97cpCnnAO_mTDzEnftDGB=OQ8G-417@mail.gmail.com>
>> BTW, rewriting that 1G file would be normal speed, since
>> the modified chunks have already been copied to the snapshot.
> i'd think that, and you'd think that, but it is not the case. most of
> my tests were done by rewriting the file 4x, and while the snap %used
> (monitored with the 'lvs' command) doesn't keep going up, performance
> stays the same.
>
i did similar tests and i saw that even though i was rewriting the file,
it appeared that the ext3 layer was reallocating new blocks. the
snapshot usage would increase to show 3x the number of blocks i had
thought it should have touched, and then it seemed to stay stable. this
is one of the problems with a block level (as opposed to file level)
snapshot.
next prev parent reply other threads:[~2010-11-15 18:08 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-12 21:52 [linux-lvm] advice for curing terrible snapshot performance? chris (fool) mccraw
2010-11-12 22:28 ` Joe Pruett
2010-11-12 23:30 ` chris (fool) mccraw
2010-11-12 23:36 ` Joe Pruett
2010-11-13 0:17 ` chris (fool) mccraw
2010-11-13 0:58 ` Stuart D Gathman
2010-11-15 17:52 ` chris (fool) mccraw
2010-11-15 18:04 ` Romeo Theriault
2010-11-15 18:08 ` Joe Pruett [this message]
2010-11-15 18:18 ` chris (fool) mccraw
2010-11-15 23:51 ` Stuart D. Gathman
2010-11-16 0:09 ` chris (fool) mccraw
2010-11-15 18:05 ` chris (fool) mccraw
2010-11-15 14:35 ` Romeo Theriault
2010-11-15 17:46 ` chris (fool) mccraw
2010-11-15 20:37 ` Stephane Chazelas
2010-11-15 22:57 ` Stuart D. Gathman
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