[mythtvnz] File System for RAID-5

[James Booth]

On Monday 15 June 2009 21:29:58 Jim Cheetham wrote:
> On Mon, Jun 15, 2009 at 2:30 PM, <james at booths.net.nz> wrote:
> > Having just had a near-death experience with my non-RAID LVM system
> > for Myth, I am about to convert everything to a RAID-5 setup (software
> > RAID) with LVM on top.
>
> Even though it's been said before on this thread, I'll say it again ...
>
> Don't use RAID-5. The failure modes you get in RAID-5 coupled with the
> disk health information available to the OS (i.e. basically none) mean
> that you stand a reasonable chance of losing all your data
> unexpectedly. RAID5 is a disk storage model based on a different
> economic value for disks/controllers to how we operate today. Don't
> use it :-)
>
> You are storing archive data, so you don't need write performance,
> just read performance. RAID1 is your simplest friend. Simplicity means
> it's quick to recover when things go wrong. And they will :-)
>
> You can have multiple disks in your RAID1 for redundancy, three would
> be plenty. Two is probably acceptable, given the delivery times for
> new disks these days. LVM on top gives the flexibility for growing &
> importing volumes, but you know that.
>
> > Before I go ahead does anyone have any
> > recommendations on best choice of file system to use, given that it
> > will be within LVM on RAID-5? I was going to go with XFS, but that
> > cannot be shrunk, which (as I have found) can be very irritating when
> > trying to reorganise your disks in an LVM.
>
> Why shrink a filesystem? I guess if you haven't figured out how you
> want to store things, perhaps ... but in general, filesystems only
> grow :-)
>
> Just stick with ext3 unless you really know the details of why you're
> using something else (yes, not very sexy is it?). XFS should be good
> by default for large objects, but you already don't like that ...
>
> -jim
>
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Well, I was orriginally considering RAID-1, the only issue being that I would 
run out of SATA ports.

I need around 3TB of working storage, and have four 1.5TB drives. I also have 
a DVD drive, giving a total of five drives. I have six SATA ports.

If I go RAID-1 then I get my 3TB, but cannot add in an extra pair of disks to 
expand storage. With RAID-5 I can add in an extra 1.5TB drive. Yes, I could 
add in another drive controller, but it all starts adding to the expense etc.

To be sure, I agree with you that RAID-1 is probably best, but while the 
"economic model" may have changed, the storage requirements have gone up 
dramatically as well.

I can see a seperate server with a bazillion TB of storage set up as RAID-10 
in my future, but probably not just yet...

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