[mythtv-users] RAID suggestions

[Nick]

On 16/11/05, Mike <stuff at dustsmoke.com> wrote:
> After using MythTV for quite some time. I'm starting to think I might
> want a raid controller to use with my 2 hitachi deskstars (250GB)
>
> I'm sort of looking at a 3ware 7506-4LP but I hear the performance isn't
> all that and its more for redudancy. I'm going for both size and speed
> since it seems a lot of the wait is in the drive, plus I want lots of
> storage. I have little faith in software raid controllers and really
> want the whole process offloaded from the CPU so it can do things like
> commflag. (hence the 3ware with good linux support)
>
> Does anybody have any suggestions to get the most speed out of my 2
> drives? Also, I am not opposed to buying 2 SATA II drives and a 3ware
> SATA controller for the backend. Is it really that big of a difference?
> Things seem slow with mythcommflag running, 3 shows recording and trying
> to bring up the recorded programs from mythweb. I plan on adding an
> HD-3000 to the mix which I hear I need almost an entire systems
> resources by itself just to watch live HDTV since it isn't HW encoded.
> And I prefer not using XvMC since the only thing I've managed to do with
> it is make the picture look worse and have the computer crash every
> couple of hours with it on.

I'd recommend thinking about potential future expansion of your
storage subsystem and how you will go about upgrading it in addition
to just wanting speed now (do you want redundancy? capacity
expansion?). Do you just want speed over the ability to restore all
your videos if a disk dies?

I'm happy at the moment running a couple of frontends and recording a
couple of shows at the same time (the datarates for SD MPEG is not
high (at 8000Kbit/s it's only 1MB/s) and my cheap Maxtor disks handle
it fine. If i was going for RAID (which I will in the future when I
get around to building a storage server) I'll likely go for at least
RAID5 with an expansion route (I think you can LVM multiple RAID sets,
but could be wrong).

IMO if you are going to go for a dedicated hardware RAID card, you
really need to use more than 2 drives to justify it. I would want both
increased speed and data protection, which would mean using at least 3
drives for RAID5. 2 drives gives you either RAID0 (increased speed
with all disk space usable) or RAID1 (full mirroring but only half the
total space available). 4 disks buys you RAID10 offering the best
speed and full mirroring (so space equal to half total drive capacity)
but at this stage I would ask myself whether RAID5 would suffice
(could use 3 disks instead of 4, still get increased speed and ability
to recover lost data via parity).

Nick