Re: howto know if raid is really working?
At Wednesday, 15 December 2004, Alvin Oga <aoga@ns.Linux-Consulting.
com> wrote:
>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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it's all so confusing.
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