Question about UNMAP command

Black, David david.black at emc.com
Wed Jan 28 10:18:55 PST 2015


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1501282_f.htm">HTML-formatted message</a>

Sorry Curtis, but you have some terms confused:

> Fully provisioned devices where all LBA’s are anchored, may still allow
LBAs to be unmapped.

What I suspect you meant to say is “Resource provisioned devices ...”

As Gerry’s original email pointed out, the anchored LBA state does not
exist in a fully provisioned device.

But Gerry isn’t asking about resource provisioned devices ...

Thanks,

--David

From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Curtis
Stevens

Sent: Wednesday, January 28, 2015 1:12 PM

To: James C Hatfield

Cc: T10 Reflector

Subject: RE: Question about UNMAP command

I don’t normally do this, but to support Jim…

Fully provisioned devices where all LBA’s are anchored, may still allow
LBAs to be unmapped.  It is important for devices of all types to be able to
take full advantage of UNMAP.  Hybrid devices are a good example of a fully
provisioned LBA space where an unmap can free-up the cache while maintaining
an anchored LBA.

There are many other examples of how unmap can help a fully provisioned
device.

When this was first brought in, I was careful about my comments on the text. 
There is nothing currently in the text that prevents this method of
operation.

-------------------------------------------------

Curtis E. Stevens

Director, Standards & Features Technology

3355 Michelson Dr. #100

Office: 1-1041

Irvine, Ca. 92612

Phone: 949-672-7933

Cell: 949-307-5050

E-Mail: Curtis.Stevens at WDC.com

Remember, you may only be blamed for something if you are actually doing
something.

From: owner-t10 at t10.org<mailto:owner-t10 at t10.org> [mailto:owner-t10 at t10.org]
On Behalf Of James C Hatfield

Sent: Wednesday, January 28, 2015 9:49 AM

Cc: T10 Reflector

Subject: Re: Question about UNMAP command

Gerry,

ATA devices are assumed to be fully provisioned, and have no restriction on
support for the DATA SET MANAGEMENT 'Trim' command.

So, by extension, fully provisioned SCSI devices should be able to support
UNMAP as well.	(Yes: I know "SCSI rules don't apply to ATA", but a precedent
has been set.)

Thank You !!!

-----------------------------------------------------------------

Jim Hatfield

Seagate Technology LLC

   e-mail:  James.C.Hatfield at seagate.com

   s-mail:  389 Disc Drive;  Longmont, CO 80503 USA

   voice:  720-684-2120

   fax....: 720-684-2711

   cell...: 720-771-8914

On Wed, Jan 28, 2015 at 8:45 AM, Gerry Houlder
<gerry.houlder at seagate.com> wrote:

Some questions have come up about whether a fully provisioned logical unit
may support the UNMAP command. SBC-4 r4 has a table (table 5) in the Logical
Block Provisioning Model that states that fully provisioned logical units are
prohibited from supporting anchored or deallocated states. The wording in
4.7.2 says a fully provisioned logical unit may support GET LBA STATUS
command but says nothing about whether UNMAP may be supported. This suggests
that a fully provisioned logical unit may support UNMAP as long as no LBAs
are anchored or deallocated. Does the group agree with this interpretation?

A reason to do this is that more host systems are using UNMAP to indicate
files they are deleting. These systems often send the UNMAP based solely on
the fact that the file is being deleted, not on the type of logical unit that
is in use. These systems would rather have a fully provisioned logical unit
act like a provisioned logical unit (i.e., accept the UNMAP command, do
nothing, and return GOOD status) than to reject the command as unsupported.
This should not be prohibited by the standard.

Another situation where this can come up is with a Host Aware ZBC device.
These devices are required to return a default initialization pattern for any
unwritten LBAs. To a host system, this looks just like those LBAs have been
unmapped by the device. Does this mean that a Host Aware device has to call
itself a resource provisioned device or can it still be a fully provisioned
device even though it appears to implement anchoring? What if that device
also accepts UNMAP commands but doesn't do anything except return GOOD status
on that command?




More information about the T10 mailing list