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Re: [linux-lvm] Will LVM2 ever be able to do striped mirrors "raid 10"? >>> Use HARDWARE RAID CONTROLLERS

On Thu, 9 Apr 2009, John Hughes wrote:

> > So if u need performance a "Software RAID Solution" would always be a bad
> > choice.
> Why?  Do you have any benchmarks that show that software raid is slower than
> hardware raid?

For RAID 1 and 0, software RAID is as fast or faster in my experience.
If you think about it, the software is just coordinating DMA transfers,
no actual processing.  It is RAID 5 and similar configurations that benefit
from hardware implementation.  My experience has been with the 'md' driver
and AIX LVM, not with Linux LVM mirroring/striping, however.

A big drawback of controller based hardware RAID is the requirement
to have same sized drives (or waste the difference).  With software RAID (and
with high end sub-system based hardware RAID), you can mix a variety of drive
sizes.  I typically use RAID 1, and I like to expand storage by just 
adding a drive in the size du jour (500G today, 1T tomorrow), and doing
a few pvmoves to expand mirrored space.  (And you can also move md
mirrors while in operation with judicious use of mdadm -a and mdadm -f,
the tricky part being no changes to a partition table while a partition is
in use).

	      Stuart D. Gathman <stuart bmsi com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.

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