Hi, *The PCIE 8x port gives me 4GBps, which is 32Gbps. No problem there. Each ESata port guarantees 3Gbps, therefore 12Gbps limit on the controller.*
I was simply listing the bandwidth available at the different stages of the data cycle. The PCIE port gives me 32Gbps. The Sata card gives me a possible 12Gbps. I'd rather be cautious and asuume I'll get more like 6Gbps, it is a cheap card after all. *I guarantee you this is not a sustainable speed for 7.2krpm sata disks.* (I am well aware :) ) * Which is 333% of the PM's capability. * Assuming that it is, 5 drives at that speed will max out my PM 3 times over. So my PM will automatically throttle the drives speed to a third of that on the account that the PM will be maxed out. Thanks for the rough IO speed check :) On Thu, Sep 9, 2010 at 3:20 PM, Edward Ned Harvey <sh...@nedharvey.com>wrote: > > 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. ;-) ) > >
_______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
