Option to skip some blocks with I/O errors during fsremap? about fstransform HOT 4 CLOSED

Hi @schellingb,

fsremap has no support to specify bad sectors, sorry.

Adding support for such a feature would be relatively straightforward,
but it would require fsremap to know the bad blocks list at start or soon after starting;
changing a (ipotetical) bad block list while running would break support for resuming an unfinished job.

Alternatively, you could hack io/io_posix.cc flush_copy_bytes() to ignore any read request (and maybe also any write request) in a certain range of the device - but this may cause a lot of missing data if part of that range happens to be used as "primary storage" (a kind of persistent buffer) by fsremap.

from fstransform.

I used dd to read around that area into /dev/null and figured a range of about 100mb that have bad blocks in it. Before and after that range dd was able to read quite large amounts of data with no issues.
I'll try to add some kind of --skip-range=a-b option in flush_copy_bytes and see how that treats me. Should be fun :-)
Thanks for the really quick response!

from fstransform.

If the disk is not too badly damaged, I found by experience that writing zeroes with dd into the bad blocks often makes them readable and writeable again (after destroying whatever data was there), so that the disk can be used for a while more. It could be worth a try.

from fstransform.

I tried writing zeroes over the bad areas but it did not seem to resolve the read errors for me.

Here's the hack I am running for now:

err = ff_log(FC_ERROR, err, "I/O error while copying " CURRENT_OP_FMT, CURRENT_OP_ARGS);
if (read_dev && dev_offset >= 1166647304ULL*512ULL - length*5 && dev_offset <= 1166710592ULL*512ULL + length*5)
{
	ff_log(FC_ERROR, 0, "    Ignoring this read error due to being known bad sector");
	err = 0;
}
else break;

And so far only one error happened:

progress: 19.6% done,   1.4 terabytes still to remap
ERROR: I/O error while copying from device to RAM, read({fd = 5, offset = 597347381248}, address + 363536384, length = 552960): Input/output error
ERROR:     Ignoring this error due to being known bad sector

I'll close this issue for now. Now that I'm not afraid of code modifications I should find my way out of this one way or another :-)

Thanks again for the hints and infos!

from fstransform.