Date: Sun, 04 Jan 2009 12:33:00 +1100 From: Andrew Snow <andrew@modulus.org> To: Pete French <petefrench@ticketswitch.com> Cc: freebsd-stable@freebsd.org Subject: Re: slow zvol performance compared to files on the same pool Message-ID: <496011CC.2010201@modulus.org> In-Reply-To: <E1LJHlS-000EO4-SB@dilbert.ticketswitch.com> References: <E1LJHlS-000EO4-SB@dilbert.ticketswitch.com>
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Pete French wrote: > I was experimenting with iscsi earlier, using both a flat file as the > backing store and also a zvol. I noticed that the zvol was giving me > dreadful performance - reading at about 20 meg/second and writing at > about 12. the fklat file gives about 45 meg/second both ways. > > i thouht it was to do wuth the iscsi layer, but I then tried it using > dd on the machinbe itself and got the same results. it seems very > curious - I am creating both the filesystem for the iscsi file and the > zvol on the same pool, so the underlying discs (4 x 15k SCSI drives on > U320) are the same in both places, as is the pool. > > anybody got any opinions ? this is on 7.1-RC2, but I have nothing else > to compare it to. On 7.x (where ZFS is really quite broken for server use - don't waste too much time on it) the ZVOL code did an "fsync" after every single block write. Its a testament to your fast disks that you got as high as 12mb/s. I don't know why your read speed was so bad, but you should try again on 8-current as numerous fixes and improvements have happened. - Andrew
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