[kwlug-disc] Media errors on a USB disk

unsolicited unsolicited at swiz.ca
Wed Oct 20 14:26:04 EDT 2010

Eric Gerlach wrote, On 10/20/2010 1:48 PM:
> On Wed, Oct 20, 2010 at 1:12 PM, Andrew Sullivan Cant
> <acant at alumni.uwaterloo.ca> wrote:
>> I have not tried SpinRite so I don't know what additional magic it might do.
> If a block is bad it reads it thousands of times with no error
> correction on then performs a statistical analysis to find out what
> the data most likely was before the block went wonky.  It uses
> different techniques (like seeking to various cylinders before
> reading) to try to get good reads.  It's pretty thorough.
> Won't help you through a head crash though.  My friend found that out
> the hard way.

Interesting, both of you.

I expect SpinRite will cause bad blocks to be marked on the drive, 
rather than e2fsck marking it in the OS. Course, if the drive ain't 
marking properly, marking it in the OS is a good thing. Unless you 
lose the inode. OTOH, if you're in to this situation, perhaps it's 
time for a new drive, sooner rather than later, anyways.

Given Eric's comments, I get a sense that SpinRite will help recover 
data, while Andrew's can help before you're into a situation where 
data has to be recovered.

http://www.grc.com/sr/spinrite.htm. Haven't used it, but have been 
aware of grc.com for years (ShieldsUp!). SpinRite at $89 (US?) ain't 
cheap though.

I don't get a sense from Khalid's message that he's convinced the 
drive has problems, or that he's lost data. Just that he's no longer 
sure of the drive - never a pleasant mindset to be in.

I suspect the only way to build confidence is to run the drive 
manufacturer's diagnostics. Then run non-USB for a while where the USB 
interface flakiness can be avoided.

My sense of USB is that it just isn't capable of passing low level 
drive instructions. So as long as all is well, all is well - as soon 
as it isn't, or may not be, it's not possible to get a grip on the 
problem, if there is a problem. OR, drive manufacturers aren't 
prepared to write diagnostic software for all permutations of OS / USB 
drivers out there.

Regardless, I think to have confidence in the drive going forward, 
it's going to have to be taken offline and dedicated diagnostic 
software run on it, for at least some period of time. Assume more than 
1 day if TB or bigger.

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