RAID questions/advise
Hi guys,
I've had a couple of RAID boxes ticking away in the corner for years now
without a problem. But now our needs have expanded, and I'm looking to
build replacements. Big replacements. And I consider myself to be
anything but an expert in the field, especially where mdadm is
concerned. So I have a few questions to ask in hopes that someone out
there can help me out.
How large of an array can mdadm handle?
If I use my hardware RAID cards in JBOD mode, how does the kernel handle
naming drives when there's more than 26 drives on the system? (i.e.
what does it do when it reaches /dev/sdz and there are drives left to be
named?)
From what I hear, ext3 can handle filesystems up to 32TB in size, but
has anyone actually done this? Can anyone attest to how well it works?
Or is there another filesystem type that's better suited to large (12TB
- 32TB) filesystems?
Finally, according to the mdadm FAQ, when a drive goes down:
19. What should I do if a disk fails?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Replace it as soon as possible:
mdadm --remove /dev/md0 /dev/sda1
halt
<replace disk and start the machine>
mdadm --add /dev/md0 /dev/sda1
Since my OS drive will not be a part of the RAID (it'll have a mirrored
RAID of it's own), I presume that the halt command won't be necessary.
I assume that it would be perfectly reasonable of me to remove the drive
and replace it while the system is running? I.e. mdadm can handle
running in degraded mode for the duration of the replacement/rebuild
process? (This is a deal-breaker question -- if mdadm can't, then I'll
have to pursue other measures. Hotswap drives will be up and running at
all times though, so I presume I can configure mdadm to make use of them
immediately upon detecting a drive failure.)
My other option is to get a SAN/NAS of some type, but building machines
like this has proven to be very effective and cheap compared to
SAN/NAS'es, at least in the past. I haven't checked recently though,
but any advice is welcome.
Pondering my options,
Michael
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