[mythtvnz] File System for RAID-5

[James Booth]

I'm starting to lean towards RAID1 or RAID10. There is one thing that I am
not clear on with RAID1, maybe someone can help me here.

 

I understand the RAID is created out of partitions, as opposed to physical
drives. Does this mean I can divide 3 x HDD's into 6 equal partitions, and
then set up a RAID-1 solution that mirrors each partition on another
partition that resides on a separate physical drive? ie I don't need an even
number of disks for a mirrored system? If so, how does adding in more disks
work? 

 

From: mythtvnz-bounces at lists.linuxnut.co.nz
[mailto:mythtvnz-bounces at lists.linuxnut.co.nz] On Behalf Of Dean Pemberton
Sent: Tuesday, 16 June 2009 11:04 a.m.
To: MythTV in NZ
Subject: Re: [mythtvnz] File System for RAID-5

 

Jim Cheetham wrote: 

On Mon, Jun 15, 2009 at 8:16 PM, Karl Leaning
<mailto:mythtv at objectivity.co.nz> <mythtv at objectivity.co.nz> wrote:
  

Umm, no with raid 5, you lose a drive not the data. add a new drive
"rebuild" the set and continue as normal...
    

 
Yes, true. Do you have a spare drive online? If you did, wouldn't you
be using it as a hot spare or part of the data set already?
 
If you lose a second drive while one drive is out of action ... you
lose data. Gone.
  

Almost everything which has been mentioned in this thread is correct.  It
just comes down to what experiences you have had in the past.

I have to agree that RAID is not a backup solution.  I run 2x 1TB USB disks
for off-site backup (no tv episodes or DVD rips make it onto these as they
are all disposable).

For data continuity on the other hand, I run the disks on my SAN in a RAID-5
set.

Recently one of the 1TB disks threw 'recoverable'[1] errors up in the kernel
log.

I called my equipment supplier and lodged an RMA.  Took 2 days.
When they had my new drive ready, I pulled the faulty drive out of the
hotswap bay[2][3] and swapped it with them.
I put the new drive in, it rebuilt, nothing missed a beat.

Now sure there are a number of things which could have gone wrong during
this process.  Most of them have been covered (second disk failing while I
had the first one out, rebuild failing, disk TOTALLY failing while waiting
for the RMA).   It is important to note however that in his case it all went
as planned.

So while people are correct to talk about potential disaster from running
RAID-5.  These are not guaranteed outcomes, sometimes it doesn't effect WAF
at all.  =)



Dean

[1]  these errors are never recoverable.  As mentioned earlier, ANY errors
are bad, replace the disk immediately.
[2]  $25 was what they cost.  Worth their weight in gold.
[3]  Always label the front of the caddy with the serial number of the disk
inside.  You can then know which drive to pull.  Otherwise if you pull the
wrong one, you may be in trouble.



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