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

[Steve Adeff]

On Friday 11 November 2005 11:57, Erik Karlin wrote:
> 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)

ah, thats how you got away with less drives!

thanks for clearing that up,

Steve