[176694] in North American Network Operators' Group
Re: Got a call at 4am - RAID Gurus Please Read
daemon@ATHENA.MIT.EDU (Allen McKinley Kitchen (gmail))
Tue Dec 9 20:15:52 2014
X-Original-To: nanog@nanog.org
In-Reply-To: <20141209222259.6742169.43034.17675@supermathie.net>
From: "Allen McKinley Kitchen (gmail)" <allenmckinleykitchen@gmail.com>
Date: Tue, 9 Dec 2014 20:15:41 -0500
To: Michael Brown <michael@supermathie.net>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
+1 on the most important statement below, from my point of view: RAID 5 and R=
AID 10 are totally separate animals and while you can set up a separate RAID=
10 array and migrate your data to it (as soon as possible!!!) you cannot mi=
grate from 5 to 10 in place absent some utter magic that I am unaware of.
10 requires more raw drive space but offers significant write performance ad=
vantages when correctly configured (which isn't really too difficult). 5 is f=
ine for protection against losing one drive, but 5 requires much more intern=
al processing of writeable data before it begins the writes and, not too lon=
g ago, was considered completely inappropriate for applications with high nu=
mbers of writes, such as a transactional database.
Still, 5 is often used for database systems in casual installations just bec=
ause it's easy, cheap (relatively) and modern fast boxes are fast enough.=20=
Ok, getting down off my RAID soapbox - good luck.
..Allen
> On Dec 9, 2014, at 17:22, Michael Brown <michael@supermathie.net> wrote:
>=20
> If the serveraid7k cards are LSI and not Adaptec based (I think they are) y=
ou should just be able to plug in a new adapter and import the foreign confi=
guration.
>=20
> You do have a good backup, yes?
>=20
> Switching to write-through has already happened (unless you specified Writ=
eBackModeEvenWithNoBBU - not the default) - these (LSI) cards =E2=80=8Eby de=
fault only WB when "safe".
>=20
> If WT, RAID10 much better perf. BUT you just can't migrate from R5 to R10 n=
on-destructively.
>=20
> - Michael from Kitchener
> Original Message =20
> From: symack
> Sent: Tuesday, December 9, 2014 16:04
> To: nanog@nanog.org
> Subject: Got a call at 4am - RAID Gurus Please Read
>=20
> Server down..... Got to colo at 4:39 and an old IBM X346 node with
> Serveraid-7k has failed. Opened it up to find a swollen cache battery that=
> has bent the card in three different axis. Separated the battery. (i)
> Inspect card and plug back in, (ii) reboot, and got (code 2807) Not
> functioning....
> Return to (i) x3 got same result. Dusted her off and let it sit for a whil=
e
> plugged in, rebooted to see if I can get her to write-through mode, disks
> start spinning. Horay.
>=20
> Plan of action, (and the reason for my post):
>=20
> * Can I change from an active (ie, disks with data) raid 5 to raid 10.
> There are 4 drives
> in the unit, and I have two on the shelf that I can plug in.
> * If so, will I have less of performance impact with RAID 10 + write-thru
> then RAID 5 + write through
> * When the new raid card comes in, can I just plug it in without loosing m=
y
> data? I would:
>=20
> i) RAID 10
> ii) Write-thru
> iii) Replace card
>=20
> The new card is probably coming with a bad battery that would put us kind
> of in square one. New batteries are 200+ if I can find them. Best case
> scenario is move it over to RAID 10+Write-thru, and feel less of the
> performance pinch.
>=20
> Given I can move from RAID 5 to RAID 10 without loosing data. How long to
> anticipate downtime for this process? Is there heavy sector re-arranging
> happening here? And the same for write-thru, is it done quick?
>=20
> I'm going to go lay down just for a little white.
>=20
> Thanks in Advance,
>=20
> Nick from Toronto.
