Re: "data=writeback" and TRIM don't get along

[Dmitry Monakhov <dmonakhov@openvz.org>]

Nebojsa Trpkovic <trx.lists@gmail.com> writes:

> On 04/08/10 03:22, Eric Sandeen wrote:
>> How does it fail?
>> 
>> Surely a bug.  :)  If you can provide details we'll look into it.
>> (perhaps it's obvious on first try but still worth saying exactly
>> what problematic behavior you saw, when reporting a bug you
>> encountered)
>
> Well, I've done a simple test, described like:
>
> "get the used sectors for a file
> hdparm --fibmap filename
> read a sector from the file eg. with
> sudo hdparm --read-sector 66385920 /dev/sda
> delete the file and sync
> rm filename;sync
> and read the sector a second time"
>
>
> And I get something like this:
>
> ================================
> # dd if=/dev/urandom of=tempfile count=100 bs=512k oflag=direct
> 100+0 records in
> 100+0 records out
> 52428800 bytes (52 MB) copied, 6.47137 s, 8.1 MB/s
>
> # hdparm --fibmap tempfile
>
> tempfile:
>  filesystem blocksize 4096, begins at LBA 0; assuming 512 byte sectors.
>  byte_offset  begin_LBA    end_LBA    sectors
>            0   37094400   37196799     102400
>
> # hdparm --read-sector 37094400 /dev/sdb
>
> /dev/sdb:
> reading sector 37094400: succeeded
> b0e8 3ad7 d080 84e8 b4b2 7e60 21f1 eff3
> 0ef9 fa10 b172 89f8 186f 0194 4cb1 e190
> d6b5 b2fe 2577 5dba e6f2 5ad7 34a0 f09f
> ca5c 07ef 6e86 c3a8 9e77 77f3 78ff 672f
> af71 dea7 ac23 a55d e31e ff83 164e bb76
> 8ea4 416d 343a 9f5e b41f b1d0 b6e9 6ed8
> 90c0 3cba ec07 1d96 fdd6 3940 1290 7cd2
> c506 c3ee c120 3732 17eb 6e68 11aa 721c...
>
> # rm tempfile
> # sync
> ================================
>
> Now, if I have "data=writeback" enable and I run
> # hdparm --read-sector 37094400 /dev/sdb
> again, I'll get the same random bytes.
> Reboot doesn't help.
>
> If I disable "data=writeback" and run
> # hdparm --read-sector 37094400 /dev/sdb
> I'll get all zeroes:
> ================================
> # hdparm --read-sector 37094400 /dev/sdb
>
> /dev/sdb:
> reading sector 37094400: succeeded
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> 0000 0000 0000 0000 0000 0000 0000 0000
> ...
> ================================
>
> So, TRIM command works well, but not with "data=writeback" mount option.
>
> Other info:
>
> Intel X25-V 40GB (latest firmware)
can you please provide an actual version of firmware.
As soon as i know X25 zeroing was disabled.
Can you please post an output of your queue flags 
cat /sys/block/sdXXX/queue/discard_zeroes_data 
>
> Linux box 2.6.33-gentoo #4 SMP Sat Apr 3 05:02:04 CEST 2010 x86_64
> Intel(R) Core(TM) i5 CPU 750 @ 2.67GHz GenuineIntel GNU/Linux
>
>
> Nebojsa
>
>
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