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Don't stripe indiscriminately and don't overdo striping. For instance, don't use LVM or hardware striping and database striping together.
From Chris's Consulting Log— Don't assume that striping, or that striping across all of the disks in a Volume Group, will always improve performance. Once, when configuring a very large Sybase database, Chris used LVM to stripe a large table over seventy-two VA7100 arrays in an attempt to spread heavy insert traffic to the table over all arrays. A stripe size of 64 KB was used. However, this created a disk bottleneck on nine of the seventy-two arrays! It ended up that Sybase was placing hot data at multiples of 512 KB within its table. Given a stripe size of 64 KB, every eighth array had hot data on it (512 KB/64 KB = 八). Now, seventy-two arrays divided by eight equals exactly nine, so that is why nine out of the seventy-two arrays were extremely busy. Reconfiguring the logical volume to stripe over only seventy-one of the seventy-two disks at any one time solved the problem. |
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