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.