?ukasz wrote: > I have a huge problem with space maps on thumper. Space maps takes over 3GB > and write operations generates massive read operations. > Before every spa sync phase zfs reads space maps from disk. > > I decided to turn on compression for pool ( only for pool, not filesystems ) > and it helps.
That is extremely hard to believe (given that all you actually did was turn on compression for a 19k filesystem). > Now space maps, intent log, spa history are compressed. All normal metadata (including space maps and spa history) is always compressed. The intent log is never compressed. > Not I'm thinking about disabling checksums. All metadata are written in 2 > copies, > so when I have compression=on do I need checksums ? Yes, you need checksums, otherwise silent hardware errors will be silent data corruption. You can not turn off checksums on metadata. Turning off checksums may have some tiny impact because it will cause the level-1 indirect blocks to compress better. > Is there other way to check space map compression ratio ? > Now I'm using "#zdb -bb pool" but it takes hours. You can probably do it with "zdb -vvv pool | less" and look for each of the space map files in the MOS. This is printed pretty early on, after which you can kill off the zdb. --matt _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
