On Tue, Apr 16, 2013 at 3:48 PM, Jay Heyl <j...@frelled.us> wrote: > My question about the rationale behind the suggestion of mirrored SSD > arrays was really meant to be more in relation to the question from the OP. > I don't see how mirrored arrays of SSDs would be effective in his > situation. >
There is another detail here to keep in mind: ZFS checks checksums on every read from storage, and with raid-zn used with block sizes that give it more capacity than mirroring (that is, data blocks are large enough that they get split across multiple data sectors and therefore devices, instead of degenerate single data sector plus parity sector(s) - OP mentioned 32K blocks, so they should get split), this means each random filesystem read that isn't cached hits a large number of devices in a raid-zn vdev, but only one device in a mirror vdev (unless ZFS splits these reads across mirrors, but even then it is still fewer devices hit). If you are limited by IOPS of the devices, then this could make raid-zn slower. Disclaimer: this is theory, I haven't tested this in practice, nor have I done any math to see if it should matter to SSDs. However, since it is a configuration question rather than a hardware question, it may be possible to acquire (some of) the hardware first and test both setups before deciding. Tim _______________________________________________ OpenIndiana-discuss mailing list OpenIndiana-discuss@openindiana.org http://openindiana.org/mailman/listinfo/openindiana-discuss
