Re: [Hampshire] Laptop Hardrive

> reallocations appear in the Linux syslog

Really? I've only ever seen summary information from smartmontools there.
I've also been unable to find anything in Google to support the idea that
actual reallocation map data goes into syslog; perhaps you'd post some
examples so we can all learn about it.

>>> So, I lost 3 sectors, so which files have 512 bytes missing?
>>
>> None of them. That's the purpose of reallocating sectors, not just
>> letting
>> them fail.
>
> That is false

No it isn't.

> a reallocation can happen if a sector fails to be
> readable any more although it is true that the drive tries to spot
> sectors that are about to turn bad, and reallocate them before they
> fail.

That leaves you with all your files intact.

> A reallocation can also happen on write, where a read after write
> check is done, and if it failed to write correctly, it instead
> reallocates the sector and writes to the new location for that same
> sector. In the "write" case, data is not lost.

So if data is not lost - all your files are intact.

In both of your examples, all your files are intact - none of them are
missing any data. That's what I said, and what you claimed was false.

> On some consumer HDs, it can silently loose data for a sector without
> warning. Reallocation is one way this happens, so sha256sum can help
> with this.

That would be a faulty drive design. Whilst I'm not going to claim that
all HDD firmware is perfect, it's the least of your worries when it comes
to HDD reliability. Reallocation routines are well-tested and fairly
similar from one model of drive to the next.

> I was talking to someone at a kernel summit and they were in charge of
> a large array of test disks. They tried doing a sha256sum on data that
> was unlikely to change and then went back 6 months later to compare
> it. They were stunned at the amount of silent data corruptions that
> had happened. Some were even single bit flips, which apparently disc
> sector CRC checking is supposed to catch, but it did not.

That proves nothing about the behaviour of the drive - only that something
has changed data on it. I regularly get customer machines in where
supposedly-invariate files have changed. That is rarely to do with disk
failure, and usually to do with a virus.

Now I'm not claiming that there are virus problems in Linux systems - just
that declaring unexpected file changes to be down to sector reallocation
faults is simply bogus; there is absolutely no evidence to support it.

> I do not remember the person who stated it, but it was made by someone
> who was trustworthy.

That renders it "bloke in a pub told me"-reliable.

Vic.