Re: [PATCH v3 0/4] Initial support for multi-actuator HDDs

Martin K. Petersen
2021-08-06T03:42:15Z

Damien,

> Single LUN multi-actuator hard-disks are cappable to seek and execute
> multiple commands in parallel. This capability is exposed to the host
> using the Concurrent Positioning Ranges VPD page (SCSI) and Log (ATA).
> Each positioning range describes the contiguous set of LBAs that an
> actuator serves.

I have to say that I prefer the multi-LUN model.

> The first patch adds the block layer plumbing to expose concurrent
> sector ranges of the device through sysfs as a sub-directory of the
> device sysfs queue directory.

So how do you envision this range reporting should work when putting
DM/MD on top of a multi-actuator disk?

And even without multi-actuator drives, how would you express concurrent
ranges on a DM/MD device sitting on top of a several single-actuator
devices?

While I appreciate that it is easy to just export what the hardware
reports in sysfs, I also think we should consider how filesystems would
use that information. And how things would work outside of the simple
fs-on-top-of-multi-actuator-drive case.

--
Martin K. Petersen Oracle Linux Engineering