> From: Hatish Narotam [mailto:hat...@gmail.com]
>
> PCI-E 8X 4-port ESata Raid Controller.
> 4 x ESata to 5Sata Port multipliers (each connected to a ESata port on
> the controller).
> 20 x Samsung 1TB HDD's. (each connected to a Port Multiplier).
Assuming your disks can all sustain 500Mbit/sec, which I find to be typical
for 7200rpm sata disks, and you have groups of 5 that all have a 3Gbit
upstream bottleneck, it means each of your groups of 5 should be fine in a
raidz1 configuration.
You think that your sata card can do 32Gbit because it's on a PCIe x8 bus.
I highly doubt it unless you paid a grand or two for your sata controller,
but please prove me wrong. ;-) I think the backplane of the sata
controller is more likely either 3G or 6G.
If it's 3G, then you should use 4 groups of raidz1.
If it's 6G, then you can use 2 groups of raidz2 (because 10 drives of
500Mbit can only sustain 5Gbit)
If it's 12G or higher, then you can make all of your drives one big vdev of
raidz3.
> According to Samsungs site, max read speed is 250MBps, which
> translates to 2Gbps. Multiply by 5 drives gives you 10Gbps.
I guarantee you this is not a sustainable speed for 7.2krpm sata disks. You
can get a decent measure of sustainable speed by doing something like:
(write 1G byte)
time dd if=/dev/zero of=/some/file bs=1024k count=1024
(beware: you might get an inaccurate speed measurement here
due to ram buffering. See below.)
(reboot to ensure nothing is in cache)
(read 1G byte)
time dd if=/some/file of=/dev/null bs=1024k
(Now you're certain you have a good measurement.
If it matches the measurement you had before,
that means your original measurement was also
accurate. ;-) )
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