[gpfsug-discuss] segment size and sub-block size

[Brian Marshall]

All,

When picking blockSize and segmentSize on RAID6 8+2 LUNs, I have see 2
optimal theories.


1) Make blockSize = # Data Disks * segmentSize
e.g. in the RAID6 8+2 case,  8 MB blockSize = 8 * 1 MB segmentSize

This makes sense to me  as every GPFS block write is a full stripe write

2) Make blockSize = 32 (number sub blocks) * segmentSize; also make sure
the blockSize is a multiple of #data disks * segmentSize

I don't know enough about GPFS to know how subblocks interact and what
tradeoffs this makes.

Can someone explain (or point to a doc) about sub block mechanics and when
to optimize for that?

Thank you,
Brian Marshall
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