[mythtv-users] Dec 2008 - State of the Art - Hard Drive Recommendations?
mythlist at assursys.co.uk
Wed Dec 17 14:00:03 UTC 2008
On Wed, 17 Dec 2008, Sandy Walsh wrote:
> Seems like this is a question that occurs pretty regularly, so let's take a
> snapshot of the "state-of-the-art" for hard drive selection. I'd love to hear
> all of your opinions on the following.
> What would you say are the most important criteria for selecting a PVR hard
> 1. Is it Interface? PATA? SATA? ATA-100, 133, 150, 300?
Newer interfaces have advantages, but mostly not sufficient to justify
adding an updated controller to an older motherboard. I use drives to match
the motherboard contollers.
> 2. Capacity? Is it simply Gigabytes per Dollar (G/$) or do drives just get
> flaky over a certain size?
I've never had a problem, but Seagate's NCQ/cache flush issues with recent
models - notably their 1.5TB drives - makes this worth keeping an eye on.
Note, however, that Seagate's current issue is a firmware problem, and
applies (to a lesser extent) to some of their smaller drives too.
Otherwise, GB/$ (or rather GB/£) is a primary consideration, especially for
a MythTV system where the bandwidth required is dwarfed by that offered by
all current drives.
> 3. Is it Mean Time Between Failure (MTBF)? Is this a meaningful metric
Lies, damned lies and statistics. However, I do place some worth in a long
warranty, and as such, have been buying exclusively Seagate drives since
2006 or so.
> 4. What about RAID? Good or Bad? Good for peace of mind, Bad for
> performance? Recommendations for/against using RAID? What about software
> raid (useless?)
I don't usually consider RAID5 (or any other parity-based RAID level), but
might consider it for a MythTV store (possibly used combined with storage
groups so that recordings that haven't been deleted from faster storage are
moved there after 30 days or so). Generally, though, drives seem cheap and
big enough to use RAID0, RAID1 or RAID10.
I prefer OS software RAID (e.g. Linux's md RAID) to both hardware RAID and
so-called 'fakeraid'. OS RAID gives much more visibility into the status of
individual drives, great performance and doesn't require continued
availability of certain hardware and can even be brought up via unusual
interfaces (e.g. external disc caddies connected via USB). The downside is
that it's a bit trickier to administer.
Hardware RAID is easiest to administer, but has additional monetary cost
(for the controller), needs availability of a duplicate compatible
controller if one experiences a failure, provides limited insight into
individual drive status and IME doesn't perform terribly well due to fairly
limited on-board CPUs (old i960 and similar designs) compared with modern
Fakeraid just strikes me as the worst of all worlds. Note that this doesn't
apply to using a fakeraid controller as a bunch of dumb PATA/SATA ports.
> 5. Rotational Speed? Is it a factor?
Nice to have, but 7200 rpm is pretty much the only affordable option for
consumer systems. Note also that higher speeds bring higher power
consumption and heat output.
> 6. Average Seek Time? Do technologies like Western Digital Intelliseek make
> any difference or just get in the way?
No idea. DVR appliances tend to use DVR-specific models, but I suspect much
of that is down to limited CPU/controller horsepower. I suspect applications
and OS-based IO scheduling can do a better job, as they have more insight
into how data is to be accessed in the future, and of the filesystem layout.
> 7. Vendors? Seagate? Western Digital? Hitachi? Samsung? Any warrenty horror
> stories? Others to consider?
Now that Seagate are reducing their warranty term to 3 years, I'll start
considering other manufacturers. I've done well with WD in the past, and
Samsung seem to be a favourite. I won't consider Maxtor (yes, I realise
they're part of Seagate these days), as every anecdote I've personally heard
of a failed drive has been one of theirs.
> 8. Cache size? Since this is mostly a Write operation activity does cache
> really affect performance? How important is a large cache?
Nice to have, and usually only adds <2% or so to the price compared with the
cheapest drive of the same size.
> What else?
> Ultimately ... what do you recommend and why?
Until the beginning of January:
- Seagate for the warranty, and hope they fix their NCQ/cache flush issue
- Sweet-spot of GB/$ for size (probably about 1TB)
- Largest buffer available
- Smallest number of platters
In the last few days, I've just bought a couple of ST31000333AS drives for a
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