[mythtv-users] RAID: full disk or partition (was: Question re: available SATA ports and linux software RAID)

[Jean-Yves Avenard]

Hi

On 24 April 2011 16:49,  <f-myth-users at media.mit.edu> wrote:

> The other advantage of using partitions is that it lets other tools
> know what's going on, which makes it less likely that a confused tool
> or a confused user will nuke a disk that's part of your RAID.

Yes, I had wondered about this but the likelihood of me running an
unknown tools on the disks of my PC is close to nil...

>
> Not using partitions makes alignment on 4K advanced-format disks
> easier, but modern tools will ask the disk, and most seem to default
> to leaving the first megabyte free if the disk answers either
> "unknown" or "512B", since so many 4K disks lie and claim to be
> 512B devices.  Modern gparted will do that for Samsung 2T's,
> for example.  In my case, I didn't bother forcing minimal alignment;
> losing the first meg of a 2T device is inconsequential and gives me
> slightly more margin if some wayward tool smashes the first few blocks.

My RAID array was made of 5 x 1.5TB Seagate Barracuda drives. Today
I've replaced the last one. The drives are less than 3 years old, but
they have all failed since but one.
I have replaced them with Samsung 2TB, Hitachi 2TB and the last to
fail last week was replaced with Seagate Green 2TB (whatever was
available at the time of failure). As I only had one 1.5TB disk left
in this array, I thought it would be a good time to also replace it
which let me use all the extra disk space.


>
> P.S.  I just had occasion to make an ext4fs on top of a RAID10; it
> appears to have correctly noticed suitable stride and stripe parameters
> from the underlying block device without me having to tell it manually.
> (dumpe2fs -h shows "RAID stride" and "RAID stripe width" parameters
> for that filesystem, which the same OS version does -not- show for an
> ext4fs on top of a non-RAID.)  This is particularly notable because
> there is an LVM on top of the RAID10, followed by a LUKS crypto layer,
> and finally the ext4fs; this shows that the info is being passed
> correctly through the layers.  [This is on Ubuntu 11.04, currently
> just-pre-release Natty.]

This RAID array is used with LVM and a JFS partition on top.
I doubt how I set up the RAID would have any effects on what the jfs
partition sees (my /data directory)

JY