[mythtv-users] Software RAID (was: Where are those new 1TB drives?)

John Drescher drescherjm at gmail.com
Thu Mar 8 16:32:45 UTC 2007


On 3/8/07, match at ece.utah.edu <match at ece.utah.edu> wrote:
> On 7 Mar 2007 at 22:08, Jim - MythTV wrote:
>
> >
> > How well does software raid work? is it worth going with? I was hoping to setup a FreeNAS
> > server, I have an old external 10 drive bay cdrom tower that I was planning on putting in3 icy
> > docs (2x 5 drive and 1 x 3 drive version (13 drives total) (if I can find a reasonable place in canada
> > that sells em) Probably go with a few
> > 5 750;s to start and fill the others as i get the cash :)
> >
> > oh couse would have to get a couple 5 port sata cards.
>
> Along time ago... In a galaxy far, far away... before the days of MythTV...
> before SATA... In the days when 20 gig hard drives ruled the day...
>
> Wanting to build a server, I gathered all my old drives into one pile. The
> largest of which was 9 gig, most were 4 gig, the smallest was only 500 megs.
> I used software RAID to build one array. There were SCSI drives, SCSI II
> drives and IDE drives, enough for about 80 gigs total, which was a lot for the
> day. If I remember correctly, the CPU was a 350 MHz AMD chip, and the
> motherboard used a VIA chipset. I used this particular motherboard over the
> others I had because it had an extra IDE controller and would run a total of 8
> IDE devices. The SCSI controller was a Tekram.
>
> I even did a write-up on this box, which floated around the web for a while.
>
> I never had so much as a hickup in about 18 months, and I was never able to
> find a way to overload it. Course, that machine was not running MythTV...
> YMMV.
>
> I can't speak for CPU overhead, and this particular box was probably not fast
> enough to act as a MythTV backend, but what I can attest to is that the
> software RAID code was rock-solid at that time, and this box worked a treat. I
> should think that unless the code has become broken since then, using
> modern SATA drives a software RAID NAS box should be just fine, as long
> as the rest of the hardware is well behaved.
>
On a modern 2GHz pc cpu overhead is 5 to 7% max in raid6. I have 10TB
of data stored on software raid6 at work on single and dual processor
opteron boxes. Read performance is nearly raid 0 for the number of
drives that actually store the data and write performance is around
the performance of 1 drive. There has been a little discussion (on
this list) about this as it really should not be this low considering
that the cpu is only being under 7% usage during the writes. My hdparm
number for a 6 drive (320GB seagate 7200.10) software raid 6 on an
asus am2 board with a 64 bit athlon 3200 processor using the 6 nvidia
mobo sata ports was around 267MB/s uncached reads.

John


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