> Matt, I agree with you. I am now confused, as I though it was better
> to separate physical Spans/Sets/groups by task, not logical
> partitions on one span/set/group by task.
When you create separate RAID arrays, these are presented to the OS as
separate physical disks, so you are _also_ creating separate logical
partitions, since you can't create standard OS-level partitions across
physical disks. It isn't really a question of physical-vs.-logical,
it's logical-vs.-physical-and-logical. I've never seen any benchmarks
that suggest that creating more arrays of the same RAID level on the
same controller gives better performance than utilizing as many drives
as possible in a single array, if the striping/spanning option is
there.
There _is_ one good reason to create separate RAID arrays of the same
RAID level hanging off the same card, and that is if you want to use
different stripe sizes for different application functions based on
the expected size pattern of disk reads and writes. This can be very
smart for some situations.
Other rationales (persuasive in some cases) are (a) to enable capacity
expansion for some application functions without affecting other
functions in any way, and (b) to allow an entire functional array to
be moved to a new controller when purchased.
If you're doing it for some other reason, like a performance boost
with a default config of each array...I don't think so. Remember also
that, even if separate arrays might otherwise be harmless, following
through with that design decision when using enclosures that can only
hold a certain number of drives can disallow, for example, RAID 10,
and force you to instead use two RAID 1 arrays that may be used
unevenly.
--Sandy
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Sanford Whiteman, Chief Technologist
Broadleaf Systems, a division of
Cypress Integrated Systems, Inc.
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