Dear FreeBSD community, many of our [2] (and Solaris [3]) users today are complaining about slow ZFS writes. One of the causes for these writes is the selection of the proper allocation method for allocation of new blocks [3] [4]. Another issue a write slowdown during TXG sync times.
Solaris 10 (and OpenSolaris up to november 2009) have the following scenario: - pool has more than 30% free space: use first fit method [1] - pool has less than 30% free space: use best fit method [1] This causes a major slowdown of the writes if we go below 30% of free space. On large pools, 30% may be terabytes of free space. OpenSolaris has changed this in November 2009 and the Oracle Storage Appliances also included the new code in Q1/2010 [1]. The source [1] states, that with this change they archieved a speedup of: "50% Improved OLTP Performance, 70% Reduced Variability, 200% Improvement on MS Exchange" I would like to issue a Call For Testing for the following 9-CURRENT patch: http://people.freebsd.org/~mm/patches/zfs/zfs_metaslab.patch To apply the patch against 8-STABLE, you need to apply the v15 update first: http://people.freebsd.org/~mm/patches/zfs/v15/stable-8-v15.patch The patch includes the following OpenSolaris onnv revisions: 10921 (partial), 11146, 11728, 12047 And covers the following Bug IDs: 6826241 Sync write IOPS drops dramatically during TXG sync 6869229 zfs should switch to shiny new metaslabs more frequently 6917066 zfs block picking can be improved 6918420 zdb -m has issues printing metaslab statistics References: [1] http://blogs.sun.com/roch/entry/doubling_exchange_performance [2] http://forums.freebsd.org/showthread.php?t=8270 [3] http://blogs.everycity.co.uk/alasdair/2010/07/zfs-runs-really-slowly-when-free-disk-usage-goes-above-80/ [4] http://blogs.sun.com/bonwick/entry/zfs_block_allocation [5] http://blogs.sun.com/bonwick/entry/space_maps _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
