Can anyone here confirm if SCSI UNMAP is supported on M550?

Interesting to think that drives may support or not support UNMap commands. I just assumed that the adapter or controller would need to support it and from there its just a simple SCSI command to the drive.
Also to note, an ESXi host will send an UNMap command during boot to check if the Controller, Array, etc supports the command. If your ESXi host says it supports it after it is fully booted, then it did receive something back from the device saying things are good.

Check to see if the M550 has a firmware update or if any of the firmware release notes suggest that they broke this function in a newer release and you may need to backrev.

Nicholas Farmer
 
Why would you want to issue an unmap to a local SSD? (honest curiosity here)
 
nicholasfarmer said:
Interesting to think that drives may support or not support UNMap commands. I just assumed that the adapter or controller would need to support it and from there its just a simple SCSI command to the drive.
Also to note, an ESXi host will send an UNMap command during boot to check if the Controller, Array, etc supports the command. If your ESXi host says it supports it after it is fully booted, then it did receive something back from the device saying things are good.

Check to see if the M550 has a firmware update or if any of the firmware release notes suggest that they broke this function in a newer release and you may need to backrev.

Nicholas Farmer
Click to expand...

I don't actually have an M550 I wanted to buy one the other while it was on sale but didn't want to take a chance and end up with another drive like the EVO that doesn't support it.
 
Modboxx said:
SCSI equivalent of the ATA TRIM
Click to expand...

Not ~quite~.
Despite what Wikipedia says, UNMAP is not a full analogue of trim (or vice versa).

Trim is telling the drive to reorganize data in the NAND cells so that it doesn't have to do a read/zero/write to replace a partially written cell (thus the performance degradation long term).

Unmap is telling a provisioned logical unit that blocks have been freed, and to do whatever it wants to with them (ignore them, blank them, free them up for TRIM-esque reorganization, etc), normally to return space to a back-end storage pool on a thin-provisioned lun.

Given the lack of TRIM support in ESXi, I suspect what you're trying to do is ~trigger~ a TRIM like effect where it fires off the reorganization. Having UNMAP support is no guarantee that such an event will happen - that's up to the drive firmware itself. UNMAP alone simply requires that the drive can actually mark the data as truly deleted. For most SSDs, the logical response would of course be trim-like actions, but that's not technically a guarantee in the spec.
 
lopoetve said:
Not ~quite~.
Despite what Wikipedia says, UNMAP is not a full analogue of trim (or vice versa).

Trim is telling the drive to reorganize data in the NAND cells so that it doesn't have to do a read/zero/write to replace a partially written cell (thus the performance degradation long term).

Unmap is telling a provisioned logical unit that blocks have been freed, and to do whatever it wants to with them (ignore them, blank them, free them up for TRIM-esque reorganization, etc), normally to return space to a back-end storage pool on a thin-provisioned lun.

Given the lack of TRIM support in ESXi, I suspect what you're trying to do is ~trigger~ a TRIM like effect where it fires off the reorganization. Having UNMAP support is no guarantee that such an event will happen - that's up to the drive firmware itself. UNMAP alone simply requires that the drive can actually mark the data as truly deleted. For most SSDs, the logical response would of course be trim-like actions, but that's not technically a guarantee in the spec.
Click to expand...

Yes! you're right, I'm hoping a manual SCSI UNMAP triggers a TRIM on an SSD.

http://www.v-front.de/2013/10/faq-using-ssds-with-esxi.html
 
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