Kums is our performance guru, so weigh that appropriately and relative to my own remarks...
Nevertheless, I still think RAID-5or6 is a poor choice for GPFS metadata. The write cache will NOT mitigate the read-modify-write problem of a workload that has a random or hop-scotch access pattern of small writes. In the end you've still got to read and write several times more disk blocks than you actually set out to modify. Same goes for any large amount of data that will be written in a pattern of non-sequential small writes. (Define a small write as less than a full RAID stripe). For sure, non-volatile write caches are a good thing - but not a be all end all solution. Relying on RAID-1 to protect your metadata may well be easier to administer, but still GPFS replication can be more robust. Doing both - belt and suspenders is fine -- if you can afford it. Either is buying 2x storage, both is 4x.
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