> [ ... ] Which brings another subject: usually hw RAID host > adapter have cache, and have firmware that cleverly rearranges > writes. Looking at the specs of the P400: [ ... ] it seems to > me that it has standard 256MB of cache, and only supports > RAID6 with a battery backed write cache (wise!). [ ... ] Uhm, looking further into the P400 an interesting detail: http://hardforum.com/showpost.php?s=c19964285e760bee47b8558ae82899d5&p=1033958051&postcount=4 «One is a stick of memory with a battery attached to it and one without. The one without is what the basic models ship with and usually has either 256 or 512Mb of memory, it supports caching for read operations only. [ ... ] You need the battery backed write cache module if you want to be able to use/turn on write caching on the array controller which makes a huge difference for write performance in general and is pretty much critical for raid 5 performance on writes.» It may be worthwhile to check if there is an enabled BBWC because if there is the BBWC the host adapter should be buffering writes up to 256MiB/512MiB and sorting them thus long inter-AG seeks should be happening only 10 or 5 times or not much more (4 times) that. Instead it may be happening that the P400 is doing write-through, which would reflect the unsorted seek pattern at the Linux->host adapter level into the host adapter->disk drive level. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
