[KLUG Hardware] Re: hardware RAID cards (was Informal Survey)

[Bryan J. Smith]

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On Wed, 2002-10-23 at 15:45, Mike Williams wrote: =20
> SRAM is faster than SDRAM I take it?  I'm a bit fuzzy on the
> difference other than SRAM doesn't lose everything when unpowered.

Not so much "faster" as in "throughput" but "faster" as in "latency."=20
It's the reason why 100MHz SRAM L2 Cache on a board is faster than
100MHz SDRAM Memory is on the same board.

DRAM memory takes, typically, 40-70ns to access, which is a 4-7 clock
cycle delay than sub-10ns SRAM, which is 0 cycle delay.  After a few
reads, those delays add up big time.

> I don't suppose you have a link to any articles at StorageReview?=20

Their review database has been trashed a few times.

> Well, at least you diminished mine a bit from giving me that article
> to proofread.  [incoming rant] I find it a bit scary that most of the
> high-end system vendors these days (Alienware, Falcon NW, Voodoo, and
> anybody else who advertises in MaxPC) build BIOS RAID 0 into most of
> their machines.  They reviewed one a couple months ago that had FOUR
> 120 gig drives in a stripe set!  Passing on the question of  why
> anybody would need 1/2 a terabyte in a workstation / game system, it
> seemed like a dumb idea to me to let any of your 4 drives take down
> the whole array like that.  For an almost $8000 system (a lot of that
> being 24 inch LCD) wouldn't another $200 for reduntant 360 gigs be
> better than a house-of-cards 480?  [end rant]Which nicely brings me to
> the main question I was hoping you could answer.  Since all out speed
> was the goal on this machine, that's the only reason I can see for not
> giving it RAID 5 with that many drives.  So any idea how much speed do
> you actually lose going from RAID 0 to RAID 5?

Depends on the number of writes.  If the writes are fairly sequential, a
3Ware Escalade card with 1-4MB of SRAM can easily handle RAID-5, and you
only lose 1 disk in efficiency, plus the small XOR overhead.  If you
have lots of random writes, then it really hurts.

Actually, I sure wish 3Ware would do RAID-4, it would be better for lots
of large, sequential writes.  I've suggested it to them before.

--=20
Bryan J. Smith, E.I.            Contact Info:  http://thebs.org
A+/i-Net+/Linux+/Network+/Server+ CCNA CIWA CNA SCSA/SCWSE/SCNA
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