Hello Nils, Thursday, September 18, 2008, 11:15:37 AM, you wrote:
NG> Hi Peter, NG> Sorry, I have read you post after posting a reply myself. NG> Peter Tribble wrote: >> No. The number of spindles is constant. The snag is that for random reads, >> the performance of a raidz1/2 vdev is essentially that of a single disk. (The >> writes are fast because they're always full-stripe; but so are the reads.) NG> Can you elaborate on this? NG> My understanding is that with RAIDZ the writes are always full-stripe for as NG> much data as can be agglomerated into a single contiguous write, but I thought NG> this did not imply that all of the data has to be read at once except with a NG> degraded RAID. NG> What about for instance writing 16MB chunks and reading 8K random? Wouldn't NG> RAIDZ access only the disks containing the 8K bits? Basically, the way RAID-Z works is that it spreads FS block to all disks in a given VDEV, minus parity/checksum disks). Because when you read data back from zfs before it gets to application zfs will check it's checksum (fs checksum, not a raid-z one) so it needs entire fs block... which is spread to all data disks in a given vdev. -- Best regards, Robert Milkowski mailto:[EMAIL PROTECTED] http://milek.blogspot.com _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
