[aklug] Re: adding disks to a volset.

On Tue, 20 Apr 2010, adam bultman wrote:

> Arthur, you also work with powerhouses, if memory serves. I *do* like
> the fact that with linux RAID1, you have two drives with identical,
> perfectly mountable filesystems. With hardware RAID1, I don't know
> about that; there may be other things there that might keep you from
> getting your data back.

Yes and no. While I do have some big(ger) iron lying around, 90% of our
infrastructure is still x86. Most of it in blades, too, so you're not
talking about really high-end, big footprint servers, either. Software
RAID1 makes no appreciable difference in performance for system drives, but
I don't consider local DASD a high performance storage option to begin with.
Most of my systems have an on-board Fusion MPT SCSI controller with 2.5"
73GB SCSI drives attached. For serious I/O I always go to the SAN.

My biggest motivation in sticking with software RAID is visibility. I
remember several years back working with Compaq Smart Array cards that
required a binary package just so I could see hardware events (like drive
failures) from the operating system. At least in software you'll know with
no extra software required. Mdadm catches it and sends out an alert. Very
simple, very small, very portable, and very reliable.

> As well: I've had a nightmarish number of linux software RAID problems,
> so I'm obviously biased. I've had my fair share of hardware RAID
> problems, but those were due to the previous admin being a moron (For
> example, setting up an 8 drive RAID5, and splitting the drives between
> the server and a second PC case - converting the RAID card's B channel
> from internal connector to external, running it a few feet to another PC
> case, converting it back to internal cabling, and then attaching the
> drives. But I digress.)

By all means, share. It's not likely we're all using it the same way. My
caveat is that I don't typically do RAID5 in software, but I do use RAID1
almost everywhere. And my hardware configuration actually sounds a lot
simpler than yours. You more than likely have run into some corner cases
where the general rules don't apply.

> SAN is really handy, and really zippy, too. Dual pathed 4 gig fiber
> channel to multiple high-speed spindles is nice.

:-) Life is much easier when you can manage an external storage pool rather
than a hundred discrete local DASDs.

         --Arthur Corliss
           Live Free or Die
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Received on Tue Apr 20 11:42:16 2010