In case the overhead in calculating SHA256 was the cause, I set ZFS checksums to SHA256 at the pool level, and left for a number of days. This worked fine.
Setting dedup=on immediately crippled performance, and then setting dedup=off fixed things again. I did notice through a zpool iostat that disk IO increased while dedup was on, although it didn't from the ESXi side. Could it be that dedup tables don't fit in memory? I don't have a great deal - 3GB. Is there a measure of how large the tables are in bytes, rather than number of entries? Chris -----Original Message----- From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-boun...@opensolaris.org] On Behalf Of Chris Murray Sent: 16 December 2009 17:19 To: Cyril Plisko; Andrey Kuzmin Cc: zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Troubleshooting dedup performance So if the ZFS checksum is set to fletcher4 at the pool level, and dedup=on, which checksum will it be using? If I attempt to set dedup=fletcher4, I do indeed get this: cannot set property for 'zp': 'dedup' must be one of 'on | off | verify | sha256[,verify]' Could it be that my performance troubles are due to the calculation of two different checksums? Thanks, Chris -----Original Message----- From: cyril.pli...@gmail.com [mailto:cyril.pli...@gmail.com] On Behalf Of Cyril Plisko Sent: 16 December 2009 17:09 To: Andrey Kuzmin Cc: Chris Murray; zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Troubleshooting dedup performance >> I've set dedup to what I believe are the least resource-intensive >> settings - "checksum=fletcher4" on the pool, & "dedup=on" rather than > > I believe checksum=fletcher4 is acceptable in dedup=verify mode only. > What you're doing is seemingly deduplication with weak checksum w/o > verification. I think fletcher4 use for the deduplication purposes was disabled [1] at all, right before build 129 cut. [1] http://hg.genunix.org/onnv-gate.hg/diff/93c7076216f6/usr/src/common/zfs/ zfs_prop.c -- Regards, Cyril _______________________________________________ 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
