Re: What is present situation with SAS bus drives?

Haines Brown wrote:
Periodically I find a need to up grade hardware. I've always run SCSI
bus hard disks, but at this point it looks as though the proper course
for a hardware upgrade would be to migrate from SCSI to SAS (Serial
Attached SCSI). I've culled some information on line, but certain
things still puzzle me.

One is that people originally said that one advantage of SAS over SCSI
was that it would be cheaper. Why is it that most SAS drives seem to
a lot more expensive than compatable SCSI disks? Although SAS has been
out for well over a year, there are surprisingly few SAS drives.

I don't know where you're looking, but many vendors carry SAS drives for less than a 10% price premium over SCSI. Seagate's current SCSI drives all come in SAS variants as well as 68- and 80-pin SCSI. The larger the drive, the lower the price premium, AFAICT, from a quick check of a couple of vendors.

I get the impression that one can't expect a driver for SAS disks in
the linux kernel for some time.

??? SAS drives are accessed through the kernel's SCSI subsystem. You don't need a SAS disk driver, the kernel's sd (SCSI disk) driver works.

What you do need is a driver for the SAS controller you have.

The LSI Logic LSIAS1064/LSIAS1068 controllers are listed as supported by the Fusion MPT driver in the stock kernel, and have been for quite a while by the looks of it (comments in the mpi_sas.h file go back to 2004). Other LSI Logic SAS controllers (of the MegaRAID family) are supported by the megraid driver in the stock kernel. Similarly, Adaptec's 4000 and 4800 series SAS RAID controllers are supported by the aacraid driver in the stock kernel.

[snip]
The Hitachi SAS drive comes in different models having different
bus connectors. One is the SAS, which comes with a standard 29-pin SAS
connector. But Hitachi says this connector is designed to be used with
a backplane into which drives are plugged. I assume though that one
can use the drive with a SAS cable connected to a SAS controller, such
as the LSI Logic.

I've never seen a SAS drive cabled directly. They've all been in hot swap SAS enclosures with appropriate backplanes. If you cable directly, you loose that hot swap capability. It may work without the backplane, but I'm not sure why you'd want to. (I'd stick with 68-pin SCSI in that case, personally.)
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