Re: how to control how often smartd-runner fires.

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From: "Carlos E. R." <[email protected]>
To: [email protected]
Message-ID: <[email protected]>
Subject: Re: [smartmontools-support] how to control how often smartd-runner
	fires.
References: <[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>
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In-Reply-To: <[email protected]>

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On 2017-01-19 19:25, Ray Andrews wrote:
> On 19/01/17 09:51 AM, mathog wrote:


>> but I don't think that badblocks has that ability.  Nor does smartctl
>> have a nondestructive read then write mode.  Somebody please correct m=
e
>> if I'm wrong on that point. On the other hand, if you see pending
>> sectors on a RAID disk, you're probably going to want to replace it
>> right away in any case.
> But you'd think that some whipper-snapper ace would write something. =20
> Just from what I read at that link posted yesterday it sounded like it =

> might even be scriptable.

Not that simple. Remember that smartctl doesn't do any testing; it is
the hard disk itself, via its local cpu and "bios" and memory which does
the real thing. smartctl /simply/ triggers it, and later reads the logs
to find out what was the result.

In this context, we can guess that the hard disk keeps somewhere a list
of the current bad blocks. That somewhere is not standardized (this is
an eduicated guess of mine); apparently we only have access via SMART to
read the number of bad sectors pending realocation.

>  And you'd also think that there'd be a=20
> utility that let you know which files were effected so that you could d=
o=20
> something about it.


No, this is also difficult. If the functionality exists at all it
depends on the filesystem type. Consider that the filesystem keeps an
easy to search for filename (and path), somehow, very fast. Once you
have the entry for the filename, you get also some sort of table or list
of the sectors or records where that file is stored. This is a very fast
and optimized operation.

If you want the reverse, you have to scan all directory entries and all
tables/lists of record locations, one by one, till you hit the one you
search for. This is very disk intensive and slow. Sometimes the function
does not exist at all.

I read somewhere a procedure to find the affected file on some partition
types. It must be linked somewere at the smartmontools web page, if I
recall correctly.


So it is easier to try to backup the partition, file by file. If one
contains a badblock, you will get an error, maybe a crash of the tool.
If no error, then overwrite the entire partition with zeroes, format and
restore.


>  At that  point, you'd just have to read the file to=20
> clear the error, no?  Then make your backups and all is right with the =

> world.

No, a read does not clear the error. A write with failure triggers the
relocation, automatically by the hard disk. The operating system may
know nothing except the delay.



> In my case, I think the disk got bashed when running so it trashed some=
=20
> part of the disk, but its otherwise fine, cuz it's been 77 pending=20
> sectors for literally years otherwise of course I'd just replace the th=
ing.

Run badblocks (read mode) on the entire disk.

--=20
Cheers / Saludos,

		Carlos E. R.
		(from 42.2 x86_64 "Malachite" at Telcontar)


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