[mythtv-users] An LVM'd drive died! What do I do...

[Erik Karlin]

On Thu, Oct 27, 2005 at 01:13:39PM -0400, Steve Adeff wrote:
> On Thursday 27 October 2005 12:42, Erik Karlin wrote:
> > On Thu, Oct 27, 2005 at 05:07:50PM +0100, Alexander Fisher wrote:
> > > On 10/27/05, David Bennett <davidbennett1979 at gmail.com> wrote:
> > > > I must admit you have me quite intrigued by this RAID 5.
> > > >
> > > > So heres the deal, I am going to go out and buy some disks.
> > > > Anything I need to know before I start?
> > >
> > > 250GB disks currently seem to give the most GB per $ or ?
> > >
> > > > How (and what) do I need to know to setup a software Raid 5 on my
> > > > linux? Any guides etc.?
> > >
> > > I've had quite a bit of success installing Debian with RAID and LVM
> > > configured during the install.  GRUB won't boot off RAID5 (or LVM?)
> > > but it will boot off RAID1.  Therefore, I would suggest something like
> > > this ...
> > >
> > > 3 disks sda,sdb,sdc. 3 partitions on each.
> > > sd[abc]1 small (<1GB) RAID 1 (md0) formatted ext3 and used for /boot.
> > > sd[abc]2 small formatted for swap.  Swap is automatically striped
> > > across swap partitions.  If you don't want your system to potentially
> > > crash when you have a disk failure, you can put swap over RAID 1
> > > instead.
> >
> > I've done exactly this, though I did do a raid1 for swap too.
> >
> > > sd[abc]3 remaining space, RAID 5, and one LVM PV on top of this.
> > > Create one VG and several LVs out of this, one for each of your other
> > > filesystems (/, /usr /var/mediastore etc.)  Format these XFS but don't
> > > make them bigger than they need to be, (XFS can easily grow
> > > filesystems online but doesn't support shrinking).
> >
> > Here's where I diverge, and haven't seen mentioned yet. I went the
> > raid10 route instead. with raid5, you can lose up to 1 drive in the
> > array. any more and you lose the array. With raid10 you can lose half,
> > in theory, as long as they're not in the same raid1 set. I've got 6x250g
> > disks as 3 raid1 mirrors and then raid0 the 3 raid1 arrays.
> 
> does raid10 do parity? I thought raid 10 required a backup harddrive for every 
> drive in the array?
> 
No, there is no parity in a raid 10 array. The resilence comes from the
raid1 parts(mirrors). Yes, it does require drives added in pairs, but
drives are relatively cheap. You can add raid1 arrays in degraded mode,
so in theory, you can create a raid10 array with only half the drives. I
used this to create my array with only 4 disks while I waited for the
drives to go on sale again. It's riskier, but there seem to be
"give-away" sales every couple of months.

(Sorry it took so long to reply, it ended up in my spam folder)