Michael Evans wrote:

On Sat, Dec 19, 2009 at 1:35 PM, Roger Heflin [off-list ref] wrote:

quoted

Matt Tehonica wrote:

quoted

I have a 4 disk RAID5 using a 2048K chunk size and using XFS filesystem.
 Typical file size is about 2GB-5GB. I usually get around 50MB/sec transfer
speed when writting files to the array. Is this typcial or is it below
normal?  A friend has a 20 disk RAID6 using the same filesystem and chunk
size and gets around 150MB/sec. Any input on this??

Thanks,
Matt

Speed depends on how the disks are connected to the system, and how many
disks there are per connection, and what kind of disks they are.

If your friend had a 20 disk raid6 on one 4port sata pci-32bit/33mhz card
with port multipliers his total throughput would be <110mb/second reads or
writes, if your friend had 20 disks on 10+ port pcie-x16 cards his total
possible speed would be much much higher, reads would be expected to be
18x(rawdiskrate) if the machine could handle it.

Also newer disks are faster than older disks.

1.5tb disks read/write at 125-130+ MB/second on a fast port.
1.5tb disks read/write at 75-80 MB/second on a PCI-32bit/33mhz port.
500gb disks read/write at 75-80 MB/second on a PCI-32bit/33mhz port.
250gb disks read/write at 50-55 MB/second on a fast port.

And those PCI-32bit/33mhz ports are with only a single disk, put more than
one on there, and the io rates drop...so 2 disk on pci-32bit/33mhz (old PCI)
port will have <50MB/second each no matter how fast the disk is, put 3 on
there and each disk is down to 33mhz, 4 25MB/second or less.
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Speaking of 16x 16 port cards, why is it that it's so difficult to
find an 8 or 16 port 4 or 8/16x pcie adapter?  A good 1xpci-e to 2x
SATA costs like 25 to 50 USD.  Given the reduction in duplicate
components, it should not be hard to make a card with 8 ports for 100
USD or less right?  I don't even want any intelligence, just normal
disk to PCI-E lane connectin would be fine.

I am pretty sure it is lack of need.

I believe someone mentioned supermicro has a 8 port pcie-x4 card, that 
is in the $100 range, but the driver for it is kind of new and has 
some issues at this time.