On 10/10/23 16:15, Hannes Reinecke wrote:
> On 10/10/23 08:48, Damien Le Moal wrote:
>> On 10/9/23 15:15, Hannes Reinecke wrote:
>>> On 10/9/23 02:56, charlesfdotz@xxxxxxxxxxxx wrote:
>>>> Hello,
>>>>
>>>> I would like to request a new device manager layer be added that accepts
>>>> trim requests for sectors and instead writes zeros to those sectors.
>>>>
>>>> This would be useful to deal with SMR (shingled magnetic recording) drives
>>>> that do not support trim. Currently after an SMR drive has had enough data
>>>> written to it the performance drops dramatically because the disk must
>>>> shuffle around data as if it were full and without trim support there is no
>>>> way to inform the disk which sectors are no longer used. Currently there's
>>>> no way to "fix" or reset this without doing an ATA secure erase despite
>>>> many of these disk being sold without informing customers that they were
>>>> SMR drives (western digital was sued for selling SMR drives as NAS
>>>> drives).
>>>>
>>> Gosh, no, please don't. SMR drives have a write pointer, and if the zone
>>> needs to be reset you just reset the write pointer. Writing zeroes will
>>> result in the opposite; the zone continues to be full, and no writes can
>>> happen there.
>>
>> Yes. And zone reset *is* a trim also since after a zone reset, the sectors in
>> the zone cannot be read.
>>
> On the same vein: why didn't we hook up 'wp reset' to trim/unmap?
> The code says:
>
> if (sd_is_zoned(sdkp)) {
> sd_config_discard(sdkp, SD_LBP_DISABLE);
> return count;
> }
>
> I distinctly remember to enable discards via 'wp reset' in the
> original code; what happened to it?
Hmmm... I do not recall exactly. I think it was all about being clear and to not
overload trim/discard, or scsi unmap, which at the time was not the prettiest
thing in scsi code (it got better though).
But I do prefer having zone reset separate from trim/discard, to be clear about
the fact that things are zone aligned. From the code perspective, there are only
few places were overloading trim with zone reset would simplify a little the
code. F2fs is probably the main one that comes to mind, but simplification would
be minor. So not worth the confusion I think.
>
> Cheers,
>
> Hannes
--
Damien Le Moal
Western Digital Research
