Re: SCSI target and IO-throttling

[Vladislav Bolkhovitin <vst@vlnb.net>]

Douglas Gilbert wrote:
> Vladislav Bolkhovitin wrote:
> 
>>Steve Byan wrote:
> 
> 
> <snip>
> 
>>BTW, do you have any statistic how many modern SCSI disks support those
>>features (ORDERED, ACA, UA_INTLCK_CTL, etc)? Few years ago none of
>>available for us SCSI hardware, including tape libraries, supported ACA.
>>It was not very modern for that time, though
> 
> 
> Vlad,
> Here is part of the control mode page from a
> recent SCSI disk (Cheetah 15k.4) :
> 
> # sdparm -p co /dev/sdb -ll
>     /dev/sdb: SEAGATE   ST336754SS        0003
>     Direct access device specific parameters: WP=0  DPOFUA=1
> Control mode page [PS=1]:
>   TST         0  [cha: n, def:  0, sav:  0]  Task set type
>         0: lu maintains one task set for all I_T nexuses
>         1: lu maintains separate task sets for each I_T nexus
>   TMF_ONLY    0  [cha: n, def:  0, sav:  0]  Task management functions only
>   D_SENSE     0  [cha: n, def:  0, sav:  0]  Descriptor format sense data
>   GLTSD       0  [cha: y, def:  1, sav:  0]  Global logging target save disable
>   RLEC        0  [cha: y, def:  0, sav:  0]  Report log exception condition
>   QAM         0  [cha: y, def:  0, sav:  0]  Queue algorithm modifier
>         0: restricted re-ordering; 1: unrestricted
>   QERR        0  [cha: n, def:  0, sav:  0]  Queue error management
>         0: only affected task gets CC; 1: affected tasks aborted
>         3: affected tasks aborted on same I_T nexus
>   RAC         0  [cha: n, def:  0, sav:  0]  Report a check
>   UA_INTLCK   0  [cha: n, def:  0, sav:  0]  Unit attention interlocks control
>         0: unit attention cleared with check condition status
>         2: unit attention not cleared with check condition status
>         3: as 2 plus ua on busy, task set full or reservation conflict
>   SWP         0  [cha: n, def:  0, sav:  0]  Software write protect
>   ATO         0  [cha: n, def:  0, sav:  0]  Application tag owner
>   TAS         0  [cha: n, def:  0, sav:  0]  Task aborted status
>         0: tasks aborted without response to app client
>         1: any other I_T nexuses receive task aborted
> 
> So it doesn't support UA_INTLCK ("cha: n" implies the user
> cannot change that value). QAM can be changed to allow
> unrestricted re-ordering (of task with the SIMPLE task
> attribute).
> 
> The NormACA bit in the standard INQUIRY response is 0 so
> it doesn't support ACA either.

Thanks! This is exactly what we've seen in the our small investigation. 
Perhaps, those features are really not needed, if nobody still use them.

Vlad