Nils Goroll wrote: > Hi Robert, > > >> 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. >> > > Thank you very much for correcting my long-time misconception. > > On the other hand, isn't there room for improvement here? If it was possible > to > break large writes into smaller blocks with individual checkums(for instance > those which are larger than a preferred_read_size parameter), we could still > write all of these with a single RAIDZ(2) line, avoid the RAIDx write penalty > and improve read performance because we'd only need to issue a single read > I/O > for each requested block - needing to access the full RAIDZ line only for the > degraded RAID case. > > I think that this could make a big difference for write-once read many random > access-type applications like DSS systems etc. > > Is this feasible at all? >
Someone in the community was supposedly working on this, at one time. It gets brought up about every 4-5 months or so. Lots of detail in the archives. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
