> > --- On Thu, 7/24/08, Yashpal Nagar
> <[EMAIL PROTECTED]> wrote:
> >
> >
> >> What I also want to understand is, does
hardware
> RAID
> >> system really
> >> care about data, what happens to the data if
one, add a disk into the existing logical drive? e.g logicaldrive 2, what
> if I unkmark the disk as spare,
> what happens
> to logical drive/date??
>
> Once array has been created, you cannot remove
> disk.
>
True, But you can very well remove and add hot spare
> disks.
> > You can
> > also remove even a single hot spare drive in a RAID5
> array.
> >
I was talking about removing the disk completely, you
cannot remove it and leave it there, you have to replace it.
If it was the hot spare you removed, sure you can but you
lost the hot spare function.
Yes you can remove disk replace it if server supports hot
swap. Number of disks you can remove depends on what Raid
level you are on e.g. you cannot remove more than one drive
out of Raid 1 and 5.
> > Removing one disk from Raid 5 set will cause
> array to
> > become degraded, removing 2 disks will fail the
> virtual
> > drive with loss of data.
> >
> > Correct.
> >
> >
> > I experimented a bit on this and found expanding a
> array
> > carefully
> > does't lead to any data loss. Here is what
> experimented
> ...
>
> So in theory it appears like expanding the array with
new
> disks works,
> with no data loss and you require a reboot into Linux.
My
> OS was RHEL
> 4.0 ES
Ok good explanation on expanding a Raid 0, expanding the
LVM and hence VG. I suspect this does not mean data that was
on the first drive ever got moved or distributed into
second. You didn't say if you pulled the drive out of
the bay after this expansion. I think pulling a drive out of
Raid 0 will be disastrous right away if data was distributed
on both drives. A single disk in Raid 0 has all the data on
it and hence may be functional even after you pull out the
newly added drive that did not contain any data.
LVM cannot protect you from disk failures. LVM is good
strategy if you want to dynamically expand or contract file
systems. It does not and cannot change the basic principles
of Raid levels and their meaning. No file system can protect
you if you lost 2 drives in a Raid 1 or Raid 5 system for
example.
Regards,
--Naresh Narang
_______________________________________________
ilugd mailinglist -- ilugd@lists.linux-delhi.org
http://frodo.hserus.net/mailman/listinfo/ilugd
Archives at: http://news.gmane.org/gmane.user-groups.linux.delhi
http://www.mail-archive.com/ilugd@lists.linux-delhi.org/
