[mythtv-users] LVM2 Striping Suggestions...

[Robin Smith]

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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> > >
> >
> >
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