[mythtv-users] Recording directly to RAID

Matt Emmott memmott at gmail.com
Fri Jul 27 18:56:06 UTC 2012

On Fri, Jul 27, 2012 at 2:27 PM, David Engel <david at istwok.net> wrote:

> Is anyone recording directly to RAID?  If so, what type/size, how many
> simultaneous recordings and how well does it work?
> I'm currently using 3 independent drives for recordings.  The primary
> reason to use independent drives has been to spread in-progress
> recordings across multiple spindles.  It's fairly common for me to
> have 3 or 4 simultaneous recordings and 6 is not unheard of during
> some busy parts ot the year.
> While my drives currently aren't on death's door, they are a few years
> old now and I have had a handful of scares in the last few monoths
> where various drives (or controllers) have gone wonky.  Fonrtunately,
> the wonkyness has only been temporary and I haven't lost anything of
> real importance.  Still I'm spooked enough to seriously consider
> adding some redundancy.
> The two configurations I'm primarily considering are either a 4-disk
> RAID6 array or a pair of 2-disk RAID1 mirrors.  While the RAID6
> configuration should be more reliable, in theory, I'm leaning toward
> the RAID1 configuration.  One big reason, and the reason for this
> email, is the increased seek load on all drives with RAID6 when 4 or
> more recordings are in-progress.
> I have an Apple Xserve RAID array. Two RAID 5 volumes (one 500GB disks and
one 750GB disks, all IDE), each volume connected to my ESXi server via its
own fiber cable. I then have a 2TB LUN presented as one huge VMDK disk
image to my master backend, which is a VM.

Prior to this, I had a RAID 5 array of 200GB disks on a homemade OpenFiler
machine, presented to the then-physical MBE as an iSCSI volume (I don't
recommend this, when Myth suddenly loses its disk due to an awful network
setup, it gets angry).

Before that, I had an LVM volume set up of the same 200GB disks (This was
before recording groups existed), but I'm dumb when it comes to Linux and
accidentally deleted the entire volume.

In my current configuration, things get a bit choppy when I have 3
simultaneous recordings through my HDHomeRun Prime and I try to watch a
show on a FE, but this could be due to the VM layer of obfuscation. It's
not choppy every time and as I said, I'm pretty dumb with Linux so it could
be an issue with my setup. I'm on 0.24, and I hear that 0.25 has a much
lower IO load.

How many drives do you have? RAID 1 needs two disks, RAID 6 at least three.
I'm not sure how those are your only two options. If your disks are 2TB or
larger, I highly recommend RAID 6 over RAID 5. If you lose a disk the
rebuild on arrays that large takes so long that statistically the chances
of another disk failure or a URE (UnRecoverable Error) are quite high.
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