[GLLUG] RAID1 and Debian 7.2.0 installer

John Edwards john at cornerstonelinux.co.uk
Mon Oct 14 18:00:47 UTC 2013

BOn Mon, Oct 14, 2013 at 06:27:01PM +0100, James Roberts wrote:
> On 14/10/13 17:07, John Edwards wrote:
>1;3201;0c >>I have had all sorts of "interesting" issues with accessing
> >>partitions/disks >> 2TB and have not yet got a successful general
> >>solution using single partitions (or equivalents) and any form of
> >>software RAID. The tools overall are limited in number and there's
> >>not much up to date info around.
> >
> >Basically for physical disks over 3TB
> I'd say 2 TB

Quite right, my typo. DOS/MBR style partitions are 32-bit and so the
maximum size is 2^32 512 byte blocks (2TiB or about 2.15TB). So just
about OK for 2TB disks but anything over that needs GPT partitions.

>> in size you really should use
>> GPT partitions.
> I'm having to support older CentOS (don't ask) and older fdisk just
> does not recognise GPT, many other older tools either crash or don't
> work. But we need the disk space!

Fdisk won't support GPT, but GNU Parted does and that's been in Centos
since at least version 4. Anything older than that should be retired
soon as there has been no security updates for it for quite some time
(but you probably know that).

> The issues I have had with data loss (from the disk set, not from
> backup :) were with RAID 5 on LVM where there was a weird sort of
> dependency between getting the LVM back before I could rebuild the
> RAID and everything I tried failed to resolve the issue. Twice,
> separately.

RAID really shouldn't sit on top of LVM. It should be the other way
around (disks -> RAID -> LVM). Just thinking about how RAID5 on LVM
could be made to work makes me quesy.

> LVM by itself is readily recoverable IME as is Software RAID 5;
> though I have given up using RAID 5. 10 or 6 for me!

Agreed. For any valuable data the cost of an extra disk to make
RAID6 is usually worth it.

|    John Edwards   Email: john at cornerstonelinux.co.uk    |
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