On 12/02/08 03:47, River Tarnell wrote: > hi, > > i have a system connected to an external DAS (SCSI) array, using ZFS. the > array has an nvram write cache, but it honours SCSI cache flush commands by > flushing the nvram to disk. the array has no way to disable this behaviour. > a > well-known behaviour of ZFS is that it often issues cache flush commands to > storage in order to ensure data integrity; while this is important with normal > disks, it's useless for nvram write caches, and it effectively disables the > cache. > > so far, i've worked around this by setting zfs_nocacheflush, as described at > [1], which works fine. but now i want to upgrade this system to Solaris 10 > Update 6, and use a ZFS root pool on its internal SCSI disks (previously, the > root was UFS). the problem is that zfS_nocacheflush applies to all pools, > which will include the root pool. > > my understanding of ZFS is that when run on a root pool, which uses slices > (instead of whole disks), ZFS won't enable the write cache itself. i also > didn't enable the write cache manually. so, it _should_ be safe to use > zfs_nocacheflush, because there is no caching on the root pool. > > am i right, or could i encounter problems here?
Yes you are right and this should work. You may want to check that the write cache is disabled on the root pool disks using 'format -e' + cache + write_cache + display. > > (the system is an NFS server, which means lots of synchronous writes (and > therefore ZFS cache flushes), so i *really* want the performance benefit from > using the nvram write cache.) Indeed, performance would be bad without it. > > - river. Neil. _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
