[geeks] Cheap Adaptec SATA/SAS RAID controllers announced

[Lionel Peterson]

>From: Sridhar Ayengar <ploopster at gmail.com>
>Date: 2008/05/16 Fri AM 11:20:17 EDT
>To: The Geeks List <geeks at sunhelp.org>
>Subject: Re: [geeks] Cheap Adaptec SATA/SAS RAID controllers announced

<snip>

>First of all, isn't a x16 slot that doesn't accept x8 cards broken, 
>according to the PCI-express standard?

Not according to Wikipedia ;^)

I quote:
A connection between any two PCIe devices is known as a "link", and is built up from a collection of 1 or more lanes. All devices must minimally support single-lane (x1) link. Devices may optionally support wider links composed of 2, 4, 8, 12, 16, or 32 lanes. This allows for very good compatibility in two ways:

a PCIe card will physically fit (and work correctly) in any slot that is at least as large as it is (e.g. an x1 sized card will work in any sized slot); 
a slot of a large physical size (e.g. x16) can be wired electrically with fewer lanes (e.g. x1, x4, or x8) as long as it provides the power and ground connections required by the larger physical slot size. 
In both cases, PCIe will negotiate the highest mutually supported number of lanes.

It is often not possible to place a physically larger PCIe card (e.g. a 16x sized card) into a smaller slot, even though the two would be signal-compatible if it were possible. Some motherboards have open-ended PCIe slots which allow for a physically larger card to be inserted in a smaller PCIe slot.[0]

I end the quote.

I've seen many boards that have x8 and x16 PCI Express slots, but don't have x4 wired - I don't think it's wrong, I think it's annoying. If you look at vendor sites, I think this is why thay list MB compatibility for their RAID cards (if PCI Express were implemented they way you think it should, there'd be no need for such a list IMHO).

>Also, is this card actually hardware RAID?  Adaptec cards tend to be a 
>bit of a mixed bag, with the low-end cards having their RAID functions 
>running on the system CPU through the use of a heavyweight driver. 
>(Fake RAID)

It is implemented with their ROC (Raid On a Chip) processor running at 800 MHz with 128 Meg of it's own RAM for cache/operation - I think it is implemented in "hardware" not as "fake RAID". Given the price of the card, it *should* be hardware RAID ($250 for a four drive controller that only does RAID 1, 0, and/or 10). We're getting a 16 port RAID card here at work, and it is "real RAID" and costs just under $1K (I think it's $765 + $105 for the battery backup module), so a four drive controller should cost about 1/4th that price...

Lionel

[0] http://en.wikipedia.org/wiki/PCI_Express#Hardware_protocol_summary