Disabling the write back cache. 


For SATA/PATA(IDE):
(although for SATA this only works on a recent kernel with ATA command passthrough):
 
# hdparm -W0 /dev/sda
# hdparm -W0 /dev/hda 
# blktool /dev/sda wcache off
# blktool /dev/hda wcache off 

For SCSI: 
Using sginfo(8) which is a little tedious
It takes 3 steps. For example: 

#sginfo -c /dev/sda
 which gives a list of attribute names and values 

#sginfo -cX /dev/sda
 which gives an array of cache values which you must match up with from step 1, e.g.
 0 0 0 1 0 1 0 0 0 0 65535 0 65535 65535 1 0 0 0 3 0 0 

#sginfo -cXR /dev/sda 0 0 0 1 0 0 0 0 0 0 65535 0 65535 65535 1 0 0 0 3 0 0
 allows you to reset the value of the cache attributes. 


This disabling is kept persistent for a SCSI disk. However, for a SATA/PATA
disk this needs to be done after every reset as it will reset back to the
default of the write cache enabled. And a reset can happen after reboot or on
error recovery of the drive. This makes it rather difficult to guarantee that
the write cache is maintained as disabled.