Re: new bottleneck section in wiki

[Justin Piszcz <jpiszcz@lucidpixels.com>]

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On Wed, 2 Jul 2008, Keld Jørn Simonsen wrote:

> The 66 MHz 64-bit PCI bus is capable of handling about 4 Gbit/s, or
> about 500 MB/s. This can also be a bottleneck with bigger arrays, eg a 6
> drive array will be able to deliver about 500 MB/s, and maybe you want
> also to feed a gigabyte ethernet card - 125 MB/s, totalling potentially
> 625 MB/s on the PCI bus.
>
> The PCI-Express bus v1.1 has a limit of 250 MB/s per lane per dirction,
> and that limit can easily be hit eg by a 4-drive array.
Correction, can easily be hit with two veliciraptors.
One veliciraptor for much of the read/write throughout the entire disk
is 120MiB/s and it slows down toward the middle obviously but FYI.
So two disks saturate it, I get 120MiB/s on a PCI-e x1 card but when I run two
disks on it at the same time (saturing them I only get 80-90MiB/s) on each of
them for an aggregate bandwidth of ~160MiB/s, it could be the card too.

03:00.0 RAID bus controller: Silicon Image, Inc. SiI 3132 Serial ATA Raid II Controller (rev 01)
04:00.0 RAID bus controller: Silicon Image, Inc. SiI 3132 Serial ATA Raid II Controller (rev 01)
05:00.0 RAID bus controller: Silicon Image, Inc. SiI 3132 Serial ATA Raid II Controller (rev 01)

(Not using RAID, they also act as a normal SATA controller)

Otherwise, very good write-up!

Justin.