On Sun, Dec 20, 2009 at 10:28 AM, Roger Heflin [off-list ref] wrote:

Michael Evans wrote:

quoted

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.

Wow, I had no idea these even existed (but I now know that I have to
use -really- specific search terms to find them).

The searches,

8-port pci-e OR pciexpress OR pci-express
16-port pci-e OR pciexpress OR pci-express

yield the desired results on Google's product search, though there
seems to be only one manufacturer, and only one seller currently.  I
guess most people building >6 drive arrays have the cash to waste on
limited boxed solutions or higher-end hardware controllers that
abstract the details (and often flexibility) from the system.

I'll have to remember the search for the next time I buy
upgrade/replacement hardware.
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