Thanks for the explanation/clarification. Keep up the good work!
----- Original Message ----
From: David C. Rankin <drankinatty@xxxxxxxxxxxxxxxxxx>
To: General Discusson about Arch Linux <arch-general@xxxxxxxxxxxxx>
Sent: Monday, June 15, 2009 12:48:47 AM
Subject: Re: dmraid disk failure - howto rebuild new disk - gparted hates Me :-(
Jonathan Brown wrote:
> Nice write-up.. I've never used hardware raid.. always just software raid1, but was never actually aware of all the inherent advantages software (md) raid has over the (dm) hardware raid that you spoke of. Very good information as always sir.
>
>
Thanks -- aside from all my weary typos in it ;-) dmraid isn't hardware raid.
It, like md raid, is software raid. There are not really any disadvantages to
using it over md raid. I use both. If I would have looked further into my raid
bios's ability to rebuild before I set this box up, I would have used mdraid
instead.
With this drive failure, the only issue was tracking down what needed to be
done to accommodate the device mapper label change. The fix itself was a 2
minute fix and like I said, with some hardware, you are given the opportunity
to rebuild from the good disk before you even boot the machine which is an
advantage a pure mdraid setup doesn't have. (I know my Gigabyte and Tyan boards
will let you rebuild and I think my older MSI boards will do it as well)
Both dmraid and mdraid are fantastic raid solutions. You hear people bad-mouth
software raid all the time, and the criticisms are unfounded. The read/write
performance penalty is virtually "0" on any machine faster than a 486 and the
benefit from a raid setup is definitely worth the effort. Sure, if you want to
drop $250 - $500 on a hardware controller, there is nothing wrong with that,
but if you just want the protections offered by a mirrored raid setup and the
box you are setting up is serving less than a few dozen workstation clients,
software raid is fine.
Now any raid setup isn't a substitute for backups (including an off-site
copy), but it does save a whole lot of time when a disk goes bad. In my case
S.M.A.R.T. alerted to the drive failing and I was able to replace the disk
before any data was lost. The dm label change was just another 'learning
experience' that now will not present any hassle should another disk fail in
the future. The real learning here was how "poor" the raid bios features have
gotten on MSI boards. Even on what was one of the high-end boards.
Oh well, back up and rocking with that box. Spinning 2 500G drives in Raid1 on
the first array and spinning 2 750G drives in Raid1 in the second. The amazing
part is that in todays world we are able to pack 1.25 terabytes of Raid1
storage in a PC for less than $250 in drive costs. Ten years ago, that would
have cost a small fortune.
--
David C. Rankin, J.D.,P.E.
Rankin Law Firm, PLLC
510 Ochiltree Street
Nacogdoches, Texas 75961
Telephone: (936) 715-9333
Facsimile: (936) 715-9339
www.rankinlawfirm.com
