[mythtv-users] Why RAID 5 stops working in 2009

[Travis Tabbal]

On Fri, Oct 24, 2008 at 10:11 AM, Yan Seiner <yan at seiner.com> wrote:

> If you do that, could you please post your results on line somewhere?  I'm
> in the process of getting all the pieces for a 20 disk raid box, and I
> will need to make some decisions in the next couple of weeks on how to
> structure the filesystem.  Right now it looks like 4 x 5 - 1TB disk RAID5
> at full buildout.  I'm starting with 3 1TB drives and will grow those to
> the first 5 disk RADI5 eventually.  But if ZFS can be made to grow from 3
> to 5 disks, and then then stick those 5 disk bundles together, that would
> be really cool.



I did a basic test in Virtualbox running Nexenta Core Stable (OpenSolaris
Kernel, Ubuntu runtime).

I can create a 4 device raidz and add it to an existing pool containing
another 4 device raidz. It acts like an LVM group in that the pool gets
expanded and can take advantage of the extra space.

Note that you can NOT add devices to a raidz right now. So you can't take a
3 device array and add 2 more devices to it. But you CAN stick as many raidz
devices into the same storage pool as you would like to, and create ZFS
filesystems on top of that. You can also add single devices without any
redundancy, but with 20 drives, I wouldn't. ZFS seems to grow as needed, so
it will "just work" with the new space. You can upgrade one drive at a time
in the raidz and it will resliver the data onto the replacement drive. Doing
that one at a time will allow you to go from 3x500G to 3x1TB, for example.

Right now, my plan when I get the money is to build a new system with
3x4disk SATA cages and create 2 6-disk raidz devices. The first one will be
newly purchased devices. Not sure on size. I'll copy the data over gigabit
from the existing Linux box, and after stress testing the new server, move
the old disks into the new system and create a new raidz out of the old
6x400GB array to be upgraded as needed. I may keep the 400GB based array in
a seperate pool for storing backup snapshots of important data from the main
array. Or maybe a 1TB external drive. The ESATA HD dock makes for a nice
tape-like backup system. :)

If I can compile mythbackend on that machine, which I don't see why I
couldn't, I can make it a slave backend to handle commflagging and
transcoding for me as well. With the Ubuntu runtime, they might have already
ported the packages over so I can use aptitude to install it.
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