Re: [LSF/MM/BPF TOPIC] Hybrid SMR HDDs / Zone Domains & Realms

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On 3/3/23 03:26, Bart Van Assche wrote:
> On 3/1/23 18:03, Damien Le Moal wrote:
>> But that is the issue: zones in the middle of each domain can be
>> activated/deactivated dynamically using zone activate command. So there is
>> always the possibility of ending up with a swiss cheese lun, full of hole of
>> unusable LBAs because the other domains (other LUN) activated some zones which
>> deactivate the equivalent zone(s) in the other domain.
>>
>> With your idea, the 2 luns would not be independent as they both would be using
>> LBAs are mapped against a single set of physical blocks. Zone activate command
>> allows controlling which domains has the mapping active. So activating a zone in
>> one domains results in the zone[s] using the same mapping in the other domain to
>> be deactivated.
> 
> Hi Damien,
> 
> Your reply made me realize that I should have provided more information. 
> What I'm proposing is the following:
> * Do not use any of the domains & realms features from ZBC-2.
> * Do not make any zones visible to the host before configuration of the 
> logical units has finished. Only make the logical units visible to the 
> host after configuration of the logical units has finished. Do not 
> support reconfiguration of the logical units while these are in use by 
> the host.
> * Only support active zones. Do not support inactive zones.
> * Introduce a new mechanism for configuring the logical units.

That is not how the zone domains/zone realms feature is defined. Matching this
would require specifications changes. But an even bigger problem is that this
would not work for ATA drives (ZAC-2) as the concept of LUNs does not exist.

> 
> This is not a new idea. The approach described above is already 
> supported since considerable time by UFS devices. The provisioning 
> mechanism supported by UFS devices is defined in the UFS standard and is 
> not based on SCSI commands.
> 
> Bart.
> 

-- 
Damien Le Moal
Western Digital Research




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