Re: howto know if raid is really working?
hi ya joao
On Thu, 16 Dec 2004, Joao Clemente wrote:
> Image you're using software raid and 1 disk fails. You somehow get
> alerted and , AFAIK, you
> 1 - shutdown the machine (ok, this if you don't have a hot-swap system)
> 2 - remove the failed disk
> 3 - insert a new, "fresh-from-the-store" disk
for sanity ... i always fdisk the new disk to be the same as the
remaining disk
> 4 - power-up
and sw raid will mirror the good disk onto the new disk
depending on size of your disk ( data ), it can take a day ..
if you continue to write data, while is mirroring, yo risk losing
everything ...
if the idea of mirroring was so that you can operate, 24x7x365,
than you should be using a complete server in NYC and a complete server
in LA ...
having 2 disks on one system is an oxymoronic way to (try) guarantee
24x7x365 operation with zero downtime
IDE is NOT hot swappable
SATA disk tries to be hotswappable by looking like a scsi disk ...
SCA scsi disks is hot swappable but is NOT cheap in terms of
the same sized 1TB of 4x 300GB ( $300ea ) IDE disk array
vs lots of expensive hotswap scsi disks to create 1TB of space
> Now, if this was a hardware raid solution, yes I believe the array will
> self-contruct again.
sw raid, when PROPERLY created will also resysnc/self-construct
again all by itself
> My question is if, with these steps you'll have a
> software RAID system resync'ing the array... or you need to do extra
> steps like:
no extra step is supposed to be needed except to take the old
disk out and plug in a new one
- power down would depend on if its ide or sata or scsi
and how the disk is mounted
> 5 - partition the disk with same partition layout as the removed one
probably a good idea ... to keep it the same as before
even if your enw disk is bigger than before
- use the xtra (unused) space for something else
> and only after this step the array can re-construct .. What's your
> experience on this?
no problems with sw raid ..
hw raid isn't worth a penny .. ie .. throw it away ..
but if you got a real raid controller for say $10K or $20K
where that's all the company makes is raid controllers, than
those hw raid controllers does work as advertized
- pc/pci based hw raid is a disaster waiting to happen
- hopefaully data is backed up
on other systems where last weeks data is NOT
overwritten by this weeks suspect/corrupt new data
which you find out is corrupted 2 weeks in the future
c ya
alvin
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