[mythtv-users] LVM2 Striping Suggestions...

Robin Smith 1canuck2 at gmail.com
Sun Sep 24 02:53:13 UTC 2006


AFTER buying my hardware RAID card I read a few things that implied
software RAID may actually be better (at least that hw RAID is not as
good as its cracked up to be unless you are buying a real server class
RAID controller ($$$). Your choice of CPU and the Gig of RAM should
set you up well (providing your not planning on high def) so I'd think
you'll be fine. The PVRs use little to no CPU when recording, so
Myth-wise you're not going to be taxing your CPU that much...

On 9/23/06, Andy Speagle <sidrew at gmail.com> wrote:
> Ok.. fair enough.. getting the drives is a trivial matter... and I suppose I
> can understand not wanting to lose recordings... I consider the PVR a
> convenience rather than a long term storage system for TV... but setting up
> RAID isn't that much of a stretch.
>
> The one caveat to that is that I don't have hardware RAID available to me
> for the ATA-100 drives... and while I've had much fun with linux software
> RAID setups... I'm curious if doing software RAID with this system would be
> too much...
>
> Does anyone have any insight about performance with linux RAID?
>
> Thanks,
>
> Andy
>
>
> On 9/23/06, Robin Smith < 1canuck2 at gmail.com> wrote:
> > I work in IT, so statistically, my odds may be higher. For IBM
> > Deskstar drives (Deathstar's as we used to call them), our failure
> > rate was a whopping 9% until they released new firmware. We are on
> > Western Digital Caviar drives and the failure rate is still around 4%.
> > My RAID5 array uses four Samsung Spinpoint SATA drives (which are
> > quiet). I started out with just two, LVM together as you are
> > describing, and one of the bastard drives died! I got it replaced
> > under warranty and then bit the bullet and bought two more drives and
> > a RAID card as I was not happy with the risk. The type of failure I am
> > describing are happening within the first two months of buying the
> > drive, so I think its an issue with DOA states not lifepsan stats. I
> > also have other PCs where I have been running four 80GB drives for
> > four years no problem, so I can attest to some drives also having long
> > lifespan. Unfortunately, it seems like its a gamble though. I do not
> > buy cheap drives either, these are all high quality brand name drives.
> >
> > My thought on data integrity versus performance:
> > I'll take data integrity any day. First of all, the performance you
> > will get without striping will NOT be poor, so the striping issue is
> > somewhat moot as I'd consider it uneccesary, even with four streams
> > recording and one playing back. Data integrity was one of my goals (as
> > well as quiet sexy looking HTPC), primarily because:
> > 1. It takes a long time to set up a good Mythbox and I don't want to
> > repeat the tasks in a panic when something goes wrong with a disk.
> > 2. I don't want to lose my recordings. Sure its "just" TV, but why
> > invest the time and effort to setup a PVR and record/archive stuff if
> > you don't mind if it gets lost? I would be pissed if I lost my current
> > set of recordings. I don't want to have to archive to DVD in a timely
> > fashion because I fear for the loss of data, that's just not
> > convenient for me.
> >
> > That's my perspective anyway. To sum up, I'd basically challenge you
> > with: why stripe and increase your risk of data loss when it is
> > completely uneccessary based on your current plans? You don't need the
> > striping performance, so don't bother taking the risk it brings.
> > Return one of your PVR350s, spend the money on a third 250GB disk and
> > set up RAID5. Four simultaneous recordings sounds cool, but how often
> > are there four things on at one time that you won't get through
> > timeshifting? Three is still an awesome number of simultaneous
> > recordings...
> >
> > Robin
> >
> >
> > On 9/23/06, Andy Speagle < sidrew at gmail.com> wrote:
> > > I had the same feelings about drive lifespan... and I agree that the
> data
> > > isn't exactly mission critical... anything that I would want to keep
> would
> > > be exported on DVD or <insert media here>.  I'd rather sacrifice data
> > > integrity for my media than performance...  It's going to be fun to play
> > > with this setup... as I've done this with old bt878 cards on low-end
> systems
> > > as a test... but never on real production quality equipment.
> > >
> > > Thanks.
> > >
> > > Andy
> > >
> > >
> > > On 9/23/06, Michael MacLeod <mikemacleod at gmail.com> wrote:
> > > > If these are new drives, I suspect that the lifetime of the drive is
> > > longer than the lifetime of his currect mythtv install. Maybe if you've
> been
> > > recycling the same drives through systems for the last ten years you can
> > > expect them to die on you, but seriously, two new drives are going to
> last a
> > > while.
> > > >
> > > > RAID5 for a bunch of television shows is overkill. This isn't mission
> > > critical data here, and the disks in all likelyhood are going to last at
> > > least a few years. Maybe I'm just lucky, but I've never had a drive fail
> > > inside a desktop system (I've had a laptop drive fail when the laptop
> failed
> > > to go to sleep when the lid closed and then went for a journey on the
> > > subway, but those are different circumstances). I've been running four
> of my
> > > drives for over five years now, and they still work fine. Although, at
> four
> > > years, I did start mirroring the data on another set of drives.
> > > >
> > > >
> > > >
> > > > On 9/23/06, Eric Ladner < eric.ladner at gmail.com> wrote:
> > > > > On 9/23/06, Robin Smith <1canuck2 at gmail.com> wrote:
> > > > > > Yikes! Having been burned by too many dead hard drives in my life,
> I
> > > > > > would never consider this option... you are essentially double
> your
> > > > > > chances of complete data loss.
> > > > >
> > > > > I agree completely.  Either buy another drive and do RAID5, or
> mirror
> > > > > the pair you have.  It might not happen today or tomorrow, but
> > > > > eventually, you'll loose 500GB of data when ONE of your 250GB drives
> > > > > fail.
> > > > >
> > > > > As for throughput, consider that the average show (my average anyway
> -
> > > > > I turn my settings up for better quality) is about 2.5 Gig.  That
> > > > > works out to about 650K per second.  I'd figure you'd have to have
> > > > > about 8 to 10 streams running at the same time before you'd start to
> > > > > see problems.
> > > > >
> > > > > My 0.02
> > > > > --
> > > > > Eric Ladner
> > > > > _______________________________________________
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