As I've mentioned before, RAID choices for GPFS are not so simple. Here are a couple points to consider, I'm sure there's more. And if I'm wrong, someone will please correct me - but I believe the two biggest pitfalls are:
Some RAID configurations (classically 5 and 6) work best with large, full block writes. When the file system does a partial block write, RAID may have to read a full "stripe" from several devices, compute the differences and then write back the modified data to several devices. This is certainly true with RAID that is configured over several storage devices, with error correcting codes. SO, you do NOT want to put GPFS metadata (system pool!) on RAID configured with large stripes and error correction. This is the Read-Modify-Write Raid pitfall. GPFS has built-in replication features - consider using those instead of RAID replication (classically Raid-1). GPFS replication can work with storage devices that are in different racks, separated by significant physical space, and from different manufacturers. This can be more robust than RAID in a single box or single rack. Consider a fire scenario, or exploding power supply or similar physical disaster. Consider that storage devices and controllers from the same manufacturer may have the same bugs, defects, failures.
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