1) Turning on write caching is potentially dangerous because the disk will indicate that data has been written (to cache) before it has actually been written to non-volatile storage (disk). Since the factory has no way of knowing how you'll use your T5140, I'm guessing that they set the disk write caches off by default.
2) Since ZFS "knows" about disk caches and ensures that it issues synchronous writes where required, it is safe to turn on write caching when the *ENTIRE* disk is used for ZFS. Accordingly, ZFS will attempt to turn on a disk's write cache whenever you add the *ENTIRE* disk to a zpool. If you add only a disk slice to a zpool, ZFS will not try to turn on write caching since it doesn't know whether other portions of the disk will be used for applications which are not write-cache safe. zpool create pool01 c0t0d0 <- ZFS will try to turn on disk write cache since using entire disk zpool create pool02 c0t0d0s1 <- ZFS will not try to turn on disk write cache (only using 1 slice) To avoid future disk replacement problems (e.g. if the replacement disk is slightly smaller), we generally create a single disk slice that takes up almost the entire disk and then build our pools on these slices. ZFS doesn't turn on the write cache in this case, but since we know that the disk is only being used for ZFS we can (and do!) safety turn on the write cache manually. 3) You can change the write (and read) cache settings using the "cache" submenu of the "format -e" command. If you disable the write cache where it could safely be enabled you will only reduce the performance of the system. If you enable the write cache where it should not be enabled, you run the risk of data loss and/or corruption in the event of a power loss. 4) I wouldn't assume any particular setting for FRU parts, although I believe that Sun parts generally ship with the write caches disabled. Better to explicitly check using "format -e". -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
