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

[Dirk Munk]

moroney at world.std.spaamtrap.com (Michael Moroney) wrote:
> I am not familiar with TRIM beyond what people have written here, but
> VMS already has an IO$_DSE function that erases blocks with zeroes.
> This is different from a WRITE of all zeroes as there is no data transfer
> from the CPU to the drive, the drive is simply told to erase the blocks
> with zeroes.
>

That seems to be quite similar to the TRIM facility, certainly because 
the drive is told to erase the blocks, it is not a rewrite with zeroes 
from the CPU.


> It would appear that the correct thing to do on VMS for SSD devices is to
> always initialize them with /ERASE_ON_DELETE so that whenever a file is
> deleted, it is actually erased, and the SSD does the right thing with
> them.  It knows this because it gets a DSE erase function, which the
> file system issues to devices that support it.
>
> (other erase patterns can be defined and erased blocks can be written
> multiple times for data security reasons, but that's not applicable here)
>

I don't understand this. The "erase block" command is a function of the 
drive, do you mean to say that with a HDD you can tell the drive to 
erase a block, and also specify which pattern to use?