Richard wrote: > > Untrue. The performance of a 21-disk raidz3 will be nowhere near the > performance of a 20 disk 2-way mirrror.
You know this stuff better than I do. Assuming no bus/cpu bottlenecks, a 21 disk raidz3 should provide sequential throughput of 18 disks and random throughput of 1 disk. A 20 disk 2-way mirror should provide sequential read throughput of (at best) 20 disks, sequential write throughput of (at best) 10 disks, random read throughput of between 2 and 20 disks and random write throughput of between 1 and 10 disks. At one extreme, mirrors are marginally better and at the other extreme mirrors are 10x the write and 20x the read performance. That's a wide range. > Taking this to a limit, would you say a 1,000 disk > raidz3 set is a good thing? > 10,000 disks? I don't know, maybe. Even If we accept that there is some magic X where stripes wider than X are bad, what is that X and how do we determine it? Likely, it depends on the several factors, including r/w iops (both of which can be mitigated by L2ARC and SLOG) and resilver times. If seek time was a non-issue (flash?) then there is no real case for mirrors. Mirrors can, if the data is laid out perfectly, provide sequential throughput which grows linearly with the vdev count. RAIDZN always will provide sequential throughput which grows linearly with the stripe width. Therefore, with low access time and low throughput storage (flash?), RAIDZN with very wide stripes makes an awful lot of sense. > FS is open source, feel free to modify and share your > ideas for improvement. And that's what we are doing here: sharing ideas. -- This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
