Louwtjie Burger writes:
> Hi
>
> What is the impact of not aligning the DB blocksize (16K) with ZFS,
> especially when it comes to random reads on single HW RAID LUN.
>
> How would one go about measuring the impact (if any) on the workload?
>
The DB will have a bigger in memory footprint as you
will need to keep the ZFS record for the lifespan of the DB
block.
This probably means you want to partition memory between
DB cache/ZFS ARC cache according to the ratio of DB blocksize/ZFS recordize.
Then I imagine you have multiple spindles associated with
the lun. If you're lun is capable of 2000 IOPS over a
200MB/sec data channel then during 1 second at full speed :
2000 IOPS * 16K = 32MB of data transfer,
and this fits in the channel capability.
But using say a ZFS blocks of 128K then
2000 IOPS * 128K = 256MB,
which overload the channel. So in this example the data
channel would saturate first preventing you from reaching
those 2000 IOPS. But with enough memory and data channel
throughput then it's a good idea to keep the ZFS recordize
large.
-r
> Thank you
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