NEC DVD_RW - file read problems.

[Andrew P.]

On 10/25/05, aleksandr.derevianko at ru.transport.bombardier.com
<aleksandr.derevianko at ru.transport.bombardier.com> wrote:
>
>
>
>
> Hello All,
>
> I have the following problem:
>
> OS: FreeBSD 4.11-RELEASE.
> DVD RW: acd0: DVD-R <_NEC DVD_RW ND-3500AG> at ata1-master UDMA33
>
> I use DVD R's primary for data backup. The backup data is archived and splitted on files ~500Mb size,
> which was written on DVD-R's. I have also store the MD5 sums of those files in small checksum file.
>
> The problem is: sometimes then i check content on DVD the checksum is differs. Where is no read errors on console,
> and several attempts to calculate checksum return different results.
>
>
> bash-2.05b# grep 00001 /cdrom/md5.sums
> acc8b491f03bfa01e341808773a6f94f depot.147.tar.00001
> bash-2.05b# md5 /cdrom/depot.147.tar.00001
> MD5 (/cdrom/depot.147.tar.00001) = d821bd902c4b0e9c12510f302c10ee71
>
> # File seems cached in RAM
>
> bash-2.05b# md5 /cdrom/depot.147.tar.00001
> MD5 (/cdrom/depot.147.tar.00001) = d821bd902c4b0e9c12510f302c10ee71
> bash-2.05b# umount /cdrom
>
> # After unmounting and mounting again - different (correct) checksum.
>
> bash-2.05b# !mou
> mount /cdrom
> bash-2.05b# md5 /cdrom/depot.147.tar.00001
> MD5 (/cdrom/depot.147.tar.00001) = acc8b491f03bfa01e341808773a6f94f
>
> # Now the checksum is OK.
>
> It seems for me that sometimes device correct soft read errors on media, and sometimes - does not.
>
> Does anybody have the same expirience (i.e. checksum differs without read errors) ?
>
>
> Best Regards,
> Alexander Derevyanko
>
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Проверь память. Поставь на ночь memtest или
docmemory.