[mythtv-users] Fastest RAID for HD?

[J.D.]

All people responding have good points but often seem to have differing 
goals. Let's discuss those in more depth.

Decision points for storage solutions are:
- speed (typical or minimum speed is more important than top benchmark 
results)
- reliability (what happens when stuff happens)
- expandability (can I add more storage)
- flexibility (my storage strategy doesn't work anymore - what are my 
options now)
- operational cost (typically energy consumption - rename that to green 
footprint if that's how you look at it)

Let's discuss the various options:
- Single hard drive Pata/Sata: The world is peachy. up to 1 TB of 
storage/hd, speed good for 3-4 concurrent recording/viewing streams 
(about 30MB/s with concurrency - 70MB tops), generally fast enough to 
catch up on commflagging. As reliable as a single hard drive (You 
potential loss is limited). I still have to lose a hd I bought myself, 
but there are plenty accounts of hd failure. SataII supports hot 
swapping - great for expanding an archive. Flexibility is great, too. 
Mount into file system, use links, use myth storage groups, etc. Each hd 
can go into sleep mode (saving about 60% energy) and still automatically 
wake up in about 8s.
- USB/Firewire: well, the connector limits the total throughput. Speed 
ok to run small setups (1-2 concurrent recordings, interface limits top 
speed, sometimes bandwidth needs to be shared with other USB/firewire 
devices). Good for permanent storage, very flexible in that you take it 
and plug it into another machine (take your archive along with your 
laptop?). Turn it off if you don't need it and save energy.
- LVM/software RAID: Hides the complexity of juggling independent disks. 
Can grow by adding hds (LVM can even shrink!). Need to protect against 
major loss with redundancy (RAID1/3/5/6/10). Speed benefits by accessing 
or writing data in parallel (RAID 0/5/6/10) - don't expect to increase 
speed linearly, though, with increased concurrency. Speed can be limited 
by many things - often hardware bottlenecks (shared bus). Just to 
rebuttle a comment I saw several times: Write speed of a RAID5 is n-1 
disks if the underlying hardware supports it - unfortunately that's not 
the case with most cheap mainboards.  The big drawback comes in once you 
want/need to expand and you cannot (no more pata/sata ports on 
mainboard; on more extension cards; maxed out power supply). Suddenly, 
you have a giant on your hand and reconfig/movement is tricky and time 
consuming (think days as opposed to hours). Flexibility is limited not 
only by hardware config but also by filesystem (grow/shrink available?). 
Horrible in operational costs: a raid system needs all disks to run when 
accessing data.
- NAS (these devices that you see popping up everywhere). Performance is 
terrible (rarely more than 10-15MB/s - even across gb network); they 
often use 40-50 watts for a dual drive raid setup - that's as much as 
for a whole mythtv backend

My use case: I use hard drives for archive (20GB mpeg2 movies don't fit 
on a DVD). Currently I have 8x750GB+4*320GB hds with my single server 
myth setup. I have a second computer acting as workstation that can 
hosts some hds. Both computers are equipped with sata hotplug capable 
frames. I want speed only on the regular daily activities (record, 
commflag, transcode) and a secondary storage for archive. I want the 
archive always available, but without the need of physical access 
(plugging an hd in or flipping a switch). 12 hds always on consume a lot 
of energy (~14watts each). If all run at the same time (and 24x7) it 
makes up a noticeable portion of my total energy bill (I do this 
strictly as a hobby!). I currently use a 2 HD raid0 for recordings and 
regularly (when raid0 fills up) archive to raid5 (6x750gb). I might 
split up the raid5 again because it consumes so much energy (100watts 
extra) - this allows hotplugging individual hds that are not needed 
(harder with a raid setup :-).

And - of course - there is a separate hd to run the OS...

Mark Hutchinson wrote:
> I have read a bunch of docs, but wanted to get some feedback or  
> reports of results.
>
> HD system.  firewire capture etc....  3ghz Core2Duo, 5 sata ports.
>
> I have 5-500gig sata drives for storage.
> LVM would work, but provide no RAID.  RAID 5 is too slow from what I  
> have read.
> I was thinking of also cutting up recordings ( dont mind losing ) and  
> videos ( need some redundancy or backup )
>
> Thoughts, recommendations?
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