[Tfug] Hard Drive Question

[Adrian]

On Friday 26 May 2006 18:19, Earl J Violet wrote:
> I have a hard drive with FAT32. Later I install Linux. Are the bad
> sectors found in the previous format procedure stored in the hard drive
> controller so Linux does not to write to them? I am assuming this but
> don't have any real information other than piecing together things from
> here and there.
> 

Depends what you mean by bad sectors... Hard bad sectors should be 
automatically remapped by the physical hard drive firmware. The OS is unaware 
of any such occurrence unless directly queried or the remapping is failing. 
If you are getting hard bad sectors, it means the hard drive has run out of 
remappable spare sectors and it would be best to jump ship now, try to rescue 
data, and buy a new drive.

Soft bad sectors, on the other hand, are what badblocks command (in conjuction 
with mkfs) tries to detect and format around. If you reformated the FAT32 
partion, and didn;t select the "check drive" option, then the previous soft 
bad sectors were not included in the new format. If you didn;t do a disk 
check previously and have reason to believe there might be bad sectors, then 
you should probably move your data off and reformat it again.

*Hard bad sectors are those which the drive has determined to be 
unreadable/unwritable after multiple attempts. *Soft bad sectors are those 
which the drive had problems reading, but was able to recover after several 
passes and/or CRC correction.

Using smartctl, you can investigate general disk error rates and get an idea 
of the health of the drive. Hard bad sectors will show as something like 
"Reallocated_Sector_Count" (depends on what tag the manufacturer has decided 
to use), being the actual number of physically remapped sectors. Attempts to 
read from soft bad sectors will show as something like "CRC_Read_Error" or 
"Hardware_ECC_Recovered" (since power on). It is normal to have a few soft 
errors from time to time... but if you are getting lots of "read on /dev/... 
failed, sector xxx" errors in your kernel logs, it may be time to move on (or 
atleast designate a large surrounding section of sectors as bad with 
badblocks.

There is a tool you can use to investigate hard bad sectors, querying the 
firmware for its map... if you were so inclined. It is called SCU, but it is 
hard to find these days. (It can also do fun things like low-level format 
disks, change block sizes to make standard disks into "special" 510-byte 
block disks for your Netapp, etc.).

Adrian