> 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. The write cache can also be enabled without a battery present (at considerable risk), but I insisted to get a battery. It is enabled, and it makes a noticeable difference. Without it, it’s even slower (more than factor 2). _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
