I have a system that has a large number of drives in it (45), and it's had 
a problem with banks of disks getting disconnected from it.

however, when I started looking into it today (after another sysadmin 
worked on it for a while), I found that the system is not able to access 
the partitions on the drives.

if I am reading dmesg correctly it is seeing the partitions during boot, 
and if I do 'fdisk -l' it lists all the paritions correctly, but if I try 
to do a

dd if=/dev/sdb1 of=/dev/null count=1

I get the error "dd: opening `/dev/sdb1': No such device or address"

#ls -l /dev/sdb1
brw-rw---- 1 root disk 8, 17 Nov  7  2006 /dev/sdb1

I removed udev and setup nodes manually to eliminate any possibility that 
it was a problem there.

the attachment partitions.missing.partitions is a cat of /proc/partitions

sysfs shows all the drives but none of the partitions.

if I run fdisk and do a write (which runs the ioctl to re-read the 
parition table) the system detects the partition and is able to access it 
until the next reboot.

what is going on here?

David Lang