I am almost sure that in cache things are still hydrated. There is an outstanding RFE for this, while I am not sure, I think this feature will be implemented sooner or later. And in theory there will be little benefits as most dedup'ed shares are used for archive purposes...
PS: NetApp's do have significantly bigger problems in caching department , like virtually having no L1 cache. However it's also my duty to knw where they have an advantage Br Mertol <http://www.oracle.com/> Mertol Özyöney | Storage Sales Mobile: +90 533 931 0752 Email: mertol.ozyo...@oracle.com On 12/10/11 4:05 PM, "Pawel Jakub Dawidek" <p...@freebsd.org> wrote: >On Wed, Dec 07, 2011 at 10:48:43PM +0200, Mertol Ozyoney wrote: >> Unfortunetly the answer is no. Neither l1 nor l2 cache is dedup aware. >> >> The only vendor i know that can do this is Netapp > >And you really work at Oracle?:) > >The answer is definiately yes. ARC caches on-disk blocks and dedup just >reference those blocks. When you read dedup code is not involved at all. >Let me show it to you with simple test: > >Create a file (dedup is on): > > # dd if=/dev/random of=/foo/a bs=1m count=1024 > >Copy this file so that it is deduped: > > # dd if=/foo/a of=/foo/b bs=1m > >Export the pool so all cache is removed and reimport it: > > # zpool export foo > # zpool import foo > >Now let's read one file: > > # dd if=/foo/a of=/dev/null bs=1m > 1073741824 bytes transferred in 10.855750 secs (98909962 bytes/sec) > >We read file 'a' and all its blocks are in cache now. The 'b' file >shares all the same blocks, so if ARC caches blocks only once, reading >'b' should be much faster: > > # dd if=/foo/b of=/dev/null bs=1m > 1073741824 bytes transferred in 0.870501 secs (1233475634 bytes/sec) > >Now look at it, 'b' was read 12.5 times faster than 'a' with no disk >activity. Magic?:) > >-- >Pawel Jakub Dawidek http://www.wheelsystems.com >FreeBSD committer http://www.FreeBSD.org >Am I Evil? Yes, I Am! http://yomoli.com >_______________________________________________ >zfs-discuss mailing list >zfs-discuss@opensolaris.org >http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
