ZFS makes SSDs faster than memory!

[Ivan Voras]

On 07/23/10 15:15, Attila Nagy wrote:

> When pulling this amount of data out of the machine, the disks aren't
> saturated, they are at around 10-20% of utilization according to gstat.
> BTW, remember that two RAIDZ2 in stripe isn't RAID60. In RAIDZ2 every
> read involves a full stripe (er, block) read for checksum validation,
> which means at a 128 kiB blocksize and with 12 disks in a RAIDZ2 pool,
> all disks provide their part of that 128k read.
> That's why a RAIDZ2 pool's IO performance equals of one disk's.

Yes, in case of random IOPS you are correct - and in your case it would
mean that the files are horribly fragmented (torrent downloads? :)). For
sequential IO, even RAIDZ/1/2 will give N-1/2/3 times the performance of
a single drive because prefetching will kick in.

> The disks in a normal 20-30 MiBps network load do about 30-40 read IOPS,
> you are right that they are capable of more (around 100-120).

Except for the possible fragmentation issue, I think you should get much
better throughput even with 30-40 IOPS per drive.