say how large it was. I said it was 1996, right? Things were smaller
then.)
Hot spares are the best invention *ever*. Back in 1996 they were not the
norm.
It was a simple RAID5 system. All the drives were of the same
manufacturer. That manufacturer had a bad batch. Before the replacement
drive arrived we had a second drive failure.
It was an otherwise trustworthy drive manufacturer, too. (I think
Seagate.) Everybody has a bad batch now and then, and these just managed
to slip past through.
More recently, I found out that a drive failed in one of my boxes. It's
an ancient nightmare of a Solaris box, and I fully expected to need to
type some obscure command to get the replacement drive up and in the
system. I did a little investigation and found that all the data was
already on another drive. Though I replaced the drive, the drive I added
simply became a new hot spare.
Hot spares become much more important when you deal with more data. If
I have a drive fail at 4am and I have a hotspare I can show up at the
office at my normal hours. By the time I come in, much of the data has
already been copied over to the hot-spare. I can then make a support
call during normal business hours for the replacement drive.
If you don't have at least one hot spare in your system, you need to
make sure you have 1-2 of the required drives on hand. Yeah, you could
rely upon your service contract's same-day service, but it's a lot
nicer to at least have one drive immediately on-hand. If you don't have
same-day service, you better have a pair of spare drives because you
might just need them both.
It is important to have off-site backups, though. Not just backups,
*off-site* backups. You don't want to explain what happened to the
data when there was a building fire, flooding problem, etc. There are
problems that strike that can take down your whole machine room.
You also need a disaster recovery plan that goes from a set of documents
detailing the process, backup media, and money from the insurance
coverage, and turns that back in to what you have in your machine room.
(And it needs to be doable by a replacement. -- Assume you've just been
promoted.)
Just my two cents,
Steven Black
--
Steven Black <blacks@indiana.edu> / KeyID: 8596FA8E
Fingerprint: 108C 089C EFA4 832C BF07 78C2 DE71 5433 8596 FA8E
On Mon, Jul 13, 2009 at 05:35:30PM -0400, David Ernst wrote:
> Well, I don't think I have anything very sophisticated to say, but I'm
> inclined to agree with you about the 3x RAID6. By my calculations,
> you'll get 18T that way vs. 20T in your other proposal. I don't know
> what you're storing, but this is a lot of disk space, so probably no
> one will mind that sacrifice. Meanwhile, the RAID 6 option does give
> a slight emphasis to reliability over performance, as you wanted. So,
> basically, I think I'm just saying "your reasoning makes sense to
> me".
>
> I hate to bring this up, but twice in my life I've been affected by
> the failure of entire RAID arrays... Both were high-quality hardware
> RAID setups, and people said of both failures "this is supposed to
> never happen." In short, I recommend some other kind of backup in
> addition to the RAID, because things happen, and if your organization
> is concerned enough with reliability to consider RAID 6, I wouldn't
> assume that something like this would never happen.
>
> David
>
>
> On Mon, Jul 13, 2009 at 02:45:54PM -0400, Josh Goodman wrote:
> >
> >Hi all,
> >
> >I have a 24 x 1 TB RAID array (Sun J4400) that is calling out to be initialized and I'm going round
> >and round on possible configurations. The system attached to this RAID is a RHEL 5.3 box w/
> >hardware RAID controller. The disk space will be used for NFS and a database server with a slight
> >emphasis given to reliability over performance. We will be using LVM on top of the RAID as well.
> >
> >Here are 2 initial configuration ideas:
> >
> >* RAID 50 (4x RAID 5 sets of 6 drives)
> >* RAID 60 (3x RAID 6 sets of 8 drives)
> >
> >I'm leaning towards the RAID 60 setup because I'm concerned about the time required to rebuild a
> >RAID 5 set with 6x 1 TB disks. Having the cushion of one more disk failure per set seems the better
> >route to go. I'm interested in hearing what others have to say especially if I've overlooked other
> >possibilities.
> >
> >I'm off to start simulating failures and benchmarking various configurations.
> >
> >Cheers,
> >Josh
> >
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