[Info-vax] VMS and the (lack of the) TRIM facility.

[David Froble]

Dirk Munk wrote:
> I suppose most of you will know what the TRIM facility is, but just to 
> make sure I will explain it.

<snip>

Ok, there are at least 2 scenarios.  Direct attach and SAN.  For SAN, 
such problems should be handled entirely within the SAN.  For direct 
attach, there is the question of what might be appropriate for each 
device.  Some implementations might be bad for some devices.

In some cases, I'm not sure this entire subject is the business of any 
OS.  I've got to believe that solutions would be rather tied to specific 
things implemented in the SSD hardware.

That written, I'm led to believe that proactive is better than reactive. 
  If released blocks need to be cleared, then assigning them to some 
"work file" that exists for a background task to clear the blocks, and 
then release then to the "free list", whatever that is.  No locking 
issues, only the clearing task should have access.  There would be 
locking issues, perhaps, when moving cleared blocks to the free list. 
Adding to the end of any free list might also encourage the avoidance of 
re-using certain blocks more than others.