[mythtv-users] Recording directly to RAID
joe at thefrys.com
Fri Jul 27 22:58:40 UTC 2012
> 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.
First of all... with 4 drives, a RAID 10 or 01 would be best. But do
yourself a favor and DONT USE RAID.
I ran a variety of RAID configurations over the years and have finally seen
the error of my ways.
Mythtv works best with multiple drives in it's storage groups and does a
wonderful job spreading the load out. With my arrays, I would hear the
drives thrashing as I recorded 2-3 channels, watched one recording, and had
a commflag running, the heads were all over the disks; because the array
used all of the disks for each of 5 processes. Now, with
4 independent disks, typically each disk is handling one or 2 of those
processes... which rarely taxes the drive.
Additionally, software raid has significant overhead... so a few percent of
my processor was dedicated to just handling the IO.
Finally, RAID does nothing for you if your data is corrupted. For example
I ran a transcode job on an entire season of a show and realized afterward
that the transcoded shows were unwatchable. RAID can't help you get them
back... really killed the WAF.
So I broke my arrays and now only back up the stuff I actually need (use
storage groups to keep important and unimportant recordings organized) to
an external drive using rsnapshot (highly recommended). Additionally, I
copy my database and some other important data off to an internet based
If you have 4 drives and are willing to lose 50% for redundancy... a real
backup is a far better use of that extra space than RAID will ever be.
I bought a 2TB external esata drive just for this purpose so I could use my
existing drives for recordings.... so I doubled my storage with that
purchase and improved the performance and reliability of my system at the
Recovery is easy... if I lose a drive, I can simply copy the recordings
from the backup into any of the existing storage groups, assuming there is
room... or add the backup folder to the storage group until a new drive
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