>There *IS* one limitation in the Linux SCSI subsystem that may be biting
>you -- it only addresses up to 16 devices. That's all, folks! Obviously
>this is something that has to be changed before Linux can be taken
>seriously in the high-end storage department.
There are lots of caveats to the above mentioned 16 device limit. RH6.1
(kernel 2.2.12-20) will do more than 16 devices/LUNs IF you run the
/dev/MAKEDEV script to create more devices ("out of box" stops at
/dev/sdpX).
The real killer is the limit of 4 devices on a secondary SCSI bus due to
SD_EXTRA_DEVS. I'm testing a 11.2TB subsystem for Linux compatibility.
You ever tried to hide 11.2TB behind a grand total of FOUR LUNS?!? ;)
I've heard future releases will take this to 40, but you can fit
127 devices on a FC-AL. sigh.
>However, a RAID box *SHOULD* present its dozens of devices as a single
>device to the Linux kernel... so I don't know why this would be happening.
That will depend on how you configure the "RAID box" or subsystem. If you
configure your RAID box
as one big RAID, you will see a single device. Typically each RAID on the
subsystemis presented
as a LUN. You'll get better performance by making some number of smaller
LUNs than one
humongous LUN as you can the spread the LUNs across more than one SCSI bus
(again, assuming
a high end RAID box).
Regards,
Steve
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