[Tfug] sata raid support

[Harry McGregor]

Hi Eric,

It depends on who you talk to, and what kind of write performance they
require.

The box is fed mostly with Gigabit ethernet, thus our maximum speed is
125MB/sec

We see read speeds between 250-300MB/sec and I did an unscientific DD
write test on a VM that is running on this box (Xen virtual machine),
the VM only has 1.5GB of memory, and most of it was already in use as
cache, so I doubt this was cached very much.

narvi:/home/hmcgregor# time dd if=/dev/zero of=1GB.file bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes transferred in 10.864551 seconds (98829839 bytes/sec)

real    0m10.946s
user    0m0.000s
sys     0m1.732s

hdparm against the raw array:

Eored:~# hdparm -tT /dev/md1

/dev/md1:
 Timing cached reads:   1754 MB in  2.00 seconds = 877.55 MB/sec
 Timing buffered disk reads:  772 MB in  3.01 seconds = 256.76 MB/sec

The box is a dual opteron virtual file server (running two Xen VMs right
now, soon to be 4 Xen VMs), and has about 8.2TB usable disk space.

I doubt the Raid 6 is slowing the users down at all.

                                              Harry

Eric Gearhart wrote:
> Harry,
>
> After taking a look at the disadvantages listed at
> http://linux.cudeso.be/raid.php (and to figure out what the heck RAID 6
> is) I'm curious why you guys didn't go with RAID 5+1 or something along
> those lines. Doesn't RAID 6 kill your write performance, as you're
> basically taking RAID 5's already not-so-great write performance and
> halving it? Is whatever your serving more read-intensive than write
> intensive, which justifies RAID 6?
>
> I ask because I've got a Linux software RAID 5 at the house, I'm
> deployed to Iraq, I like playing with this stuff, and I miss my TB RAID
> in Tucson :(
>
> -Eric
>
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