On Thu, 29 Mar 2007 at 12:13pm, John R Pierce wrote
chrism@xxxxxxxxx wrote:
Joshua Baker-LePain wrote:
You know, the whole "disk is cheap, so why use RAID5?" argument just
doesn't wash with me. Sure, disk *is* cheap. But some of us need every
GB we can get for our money (well, given I'm spending grant money, it's
actually *your* money too (if you live in the US)).
To demonstrate, let's look at a 24 drive system (3ware has a 24 port 9650
board). Newegg has 500GB WD RE2 drives for $160. So for $3840 in drives
I can get:
a) 6TB RAID10 => $0.64/GB
or
b) 10.5TB RAID6 w/ hot spare => $0.37/GB
Umm, I'll take 75% more space for the same money, TYVM.
did those prices factor in the drive bay infrastructure for 24 drives with
cabling, redundant power supplies, etc?
Given 3840=160*24, no. ;) But those prices would be the same however you
configure the drives.
btw, I would NOT build a 20-something raid5/6 set. the rebuild times would
be massively slow, opening a large window for double drive failure.
Before you say 'nah, would never happen', check out phpbb.com, they lost
their web server and forums to a double failure last month, and yes, they had
a hotspare so the rebuild started immediately.
The large SAN vendors usually don't recommend building raid5 sets larger than
6-8 disks, and will stripe or concatenate multiple of those on the typical
SAN with 100s of spindles. Myself, I'll stick with RAID10 for anything
critical.
Would that I had the money to and still get the space I need. Even doing
2 12 disk RAID6 sets (each with a hot spare) gets you 9TB which is 50%
more space for the same money as RAID10.
To try to cut this debate short (hah!), this all boils down to a simple
CBA. For me, I need massive amounts of fairly reliable, fairly fast space
at as good a price as I can manage. RAID5/6 on systems backed up to tape
(oops, I seem to be crossing threads) fulfills those requirements. For
me. YMMV. No guarantees. Offer not valid in NV or NY. Do not taunt
Happy Fun Ball(TM).
--
Joshua Baker-LePain
Department of Biomedical Engineering
Duke University
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