ZFS let you do that and in case of a Slog or L2Arc there may be a single reason behind (=save money) but in general you only complicate things without an advantage, more or less you are asking for troubles only - especially if you partition datadisks in a pool. On problems there is a good chance that do something stupid.Question(s) relating to ZFS using 'whole disk' -vs- 'partitions'.
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Instead of a two whole disk mirror, what if you partitioned each of the SSDs, lets say, in to two partitions.
And then created a RAID1+0 set, where you mirror the 1st two partitions, and the 2nd two partitions and then stripe across.
Thus providing more vDEVs to the underlying scheduler, and potentially using more internal drive controller threads.
I know for HDDs this is considered a no-no ..
A good SSD with steady load can give you up to 500 MB/s write and 4ok iops with smaller blocksize. If you partition the same disk with a steady load on both partitions, you will be limited by the same overall SSD values, means that the performance is divided between both partitions, overall will be the same.
If you use a setup with many HBAs, there may be reason to assign disks in a way that a single HBA is allowed to fail and the pool keeps online (Sun did that as well). From a performance view it does not matter.
Mostly you add complexity without a serious reason.
The most important goal must be "keep it simple" as this is what helps on troubles.
btw
You should use the S3700 for Slog
Do not use the term raid-5/6 for ZFS software raid.
ZFS is more advanced, the correct terms are raid Z1 and Z2
(you can use raid-5/6 for ZFS but you will loose any repair options then)
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