On 07.06.2011 05:33, Matthew Dillon wrote:
The absolute cheapest solution is to buy a Sil-3132 PCIe card
(providing 2 E-SATA ports), and then connect an external port multiplier
to each port. External port multiplier enclosures typically support
5 drives each so that would give you your 10 drives.
Even the 3132 is a piss-ant little card it does support FIS-Based
switching so performance will be very good... it will just be limited
to SATA-II speeds is all.
SiI3132 is indeed good for it's price and it is quite good for random
I/O. But at burst speeds it is limited lower then SATA-II. Even lower
then PCIe 1.0 x1 it uses. IIRC I've seen about 150MB/s from one port and
about 170MB/s from two.
If burst rate is important, SiI3124 chip is much better -- up to about
900MB/s measured from 4 ports. The only issue is PCI-X interface: either
motherboard with PCI-X needed, or card with PCIe x8 bridge (like these
http://www.addonics.com/products/host_controller/adsa3gpx8-4e.asp), but
last case is too expensive.
There are also much cheaper (~$50) PCIe x1 bridge SiI3124 cards
(http://www.sybausa.com/productInfo.php?iid=537). They are not so fast
-- about 200MB/s, but still more then SiI3132. And they still have 4
SATA ports.
For SSDs you want to directly connect the SSD to a mobo SATA port and
then either mount the SSD in the case or mount it in a hot-swap gadget
that you can screw into a PCI slot (it doesn't actually use the PCI
connector, just the slot). A SATA-III port with a SATA-III SSD really
shines here and 400-500 MBytes/sec random read performance from a single
SSD is possible, but it isn't an absolute requirement. A SATA-II port
will still work fine as long as you don't mind maxing out the bandwidth
at 250 MBytes/sec.
Agree. Intel on-board ports rock! Recently I've built new system with
two OCZ Vertex 3 SSDs connected to 6Gbps SATA ports on Intel Sandy
Bridge class motherboard. UFS on top of graid RAID0 volume gives me
about 950MB/s on both read and write!
To get robust hot-swap enclosures you either need to go with SAS or you
need to go with discrete SATA ports (no port multiplication), and the
ports have to support hot-swap. The best hot-swap support for an AHCI
port is if the AHCI chipset supports cold-presence-detect (CPD), and
again Mobo AHCI chipsets usually don't. Hot-swap is a bit hit or miss
without CPD because power savings modes can effectively prevent hot-swap
detect from working properly. Drive disconnects will always be detected
but drive connects might not be.
I would say it depends. In some cases it is easier to detect hot-plug
then hot-unplug, as device sends COMINIT that should wake up port even
from power-save state. With ICH10, for example, I've managed to make
both hot plug and unplug work even with power-management enabled:
hot-plug via tracking COMINIT, unplug via it's CPD capability. Without
PM it "just works". :)
--
Alexander Motin
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