Are large RAID stripe sizes useful with FreeBSD?

Scott Long scottl at
Mon Mar 31 13:32:51 PDT 2008

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

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).


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