Ivan Voras wrote: > Most of new hardware RAID controllers offer stripe sizes of 128K, 256K > and some also have 512K and 1M stripes. In the simplest case of RAID0 of > two drives, knowing that the data is striped across the drives and that > FreeBSD issues IO request of at most 64K, is it useful to set stripe > sizes to anything larger than 32K? I suppose something like TCQ would > help the situation but does anyone know how is this situation usually > handled on the RAID controllers? Large I/O sizes and large stripe sizes only benefit benchmarks and a narrow class of real-world applications. Large stripes have the potential to actually hurt RAID-5 performance since they make it much harder for the card to a full stripe replacement instead of a read-modify-xor-write. I hate to be all preachy and linux-like and tell you want you need or don't need, but in all honesty, large i/o's and stripes usually don't help typical filesystem-based mail/squid/mysql/apache server apps. I do have proof-of-concept patches to allow larger I/O's for selected controllers on 64-bit FreeBSD platforms, and I intend to clean up and commit those patches in the next few weeks (no, I'm not ready for nor looking for testers at this time, sorry). ScottReceived on Mon Mar 31 2008 - 18:32:51 UTC
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