> Hi Bill, ...
lots of small files in a > largish system with presumably significant access > parallelism makes RAID-Z a non-starter, > Why does "lots of small files in a largish system > with presumably > significant access parallelism makes RAID-Z a > non-starter"? > thanks, > max Every ZFS block in a RAID-Z system is split across the N + 1 disks in a stripe - so not only do N + 1 disks get written for every block update, but N disks get *read* on every block *read*. Normally, small files can be read in a single I/O request to one disk (even in conventional parity-RAID implementations). RAID-Z requires N I/O requests spread across N disks, so for parallel-access reads to small files RAID-Z provides only about 1/Nth the throughput of conventional implementations unless the disks are sufficiently lightly loaded that they can absorb the additional load that RAID-Z places on them without reducing throughput commensurately. - bill This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
