ZFS performance bottlenecks: CPU or RAM or anything else?

[Alex Tutubalin]

On 5/18/2016 12:11 AM, Steven Hartland wrote:
> Raidz is limited essential limited to a single drive performance 
> per dev for read and write while mirror is single drive performance 
> for write its number of drives for read. Don't forget mirror is not 
> limited to two it can be three, four or more; so if you need more read 
> throughput you can add drives to the mirror.

Do I understand it correctly:

  - single write of one large file (or singe local write to zvol shared 
via iSCSI) will be local: single or only several metaslabs

  - for RAIDZ each disk will get only part of throughput

  - for mirror, each disk included in write will receive full data size 
(and for single local write only limited number of disks to be included 
in write)

If so, raidz will have huge write performance benefit in my case: single 
write of one large file.

As for read speed, I hope to deal with it with large enough L2ARC on SSDs.


>
> To increase raidz performance you need to add more vdevs. While this 
> doesn't have to be double i.e. the same vdev config as the first it 
> generally a good idea.

Again, multiple vdevs will help for multiple parallel writes, but not 
for single one?

Alex Tutubalin