blkdiscard vs hdparm for erasing a SSD?

[Peter Wu]

Hi,

Recent versions of util-linux have a blkdiscard program. How does this compare
to the --security-erase option of hdparm? The goal is to erase the contents of
an previously used SSD to improve performance.

Is the command `blkdiscard -s /dev/sdd` equivalent to the instructions listed on
https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase?

[Tim Small]

[ blkdiscard vs hdparm --security-erase] How does this compare. The goal is to erase the contents of an previously used SSD to improve performance.

When you use blkdiscard, the SSD (assuming a SATA SSD) will receive an
ATA TRIM command, whereas hdparm --security-erase will issue an ATA
SECURITY ERASE UNIT command.

What the drive then actually does is dependant on the implementation
details of that particular SSD's firmware.

In general, I would expect the performance gain from TRIMing the entire
drive to be either the same-as, or possibly less-than the gain from
SECURITY ERASE. For a sane firmware implementation I'd expect them to
have the same effect on performance. Firmware implementations are not
always sane.

Personally, unless I want to keep some of the data on the drive, I use
hdparm --security-erase, as I feel that this is most likely to reset the
drive to its as-new state (or at least close to it), but the real answer
is that it depends on the drive, so if you really want to know, you'll
have to do some performance tests on your drive(s).

Tim.
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[Peter Wu]

Post by Tim Small

[ blkdiscard vs hdparm --security-erase] How does this compare. The goal is
to erase the contents of an previously used SSD to improve performance.

When you use blkdiscard, the SSD (assuming a SATA SSD) will receive an
ATA TRIM command, whereas hdparm --security-erase will issue an ATA
SECURITY ERASE UNIT command.
What the drive then actually does is dependant on the implementation
details of that particular SSD's firmware.
In general, I would expect the performance gain from TRIMing the entire
drive to be either the same-as, or possibly less-than the gain from
SECURITY ERASE. For a sane firmware implementation I'd expect them to
have the same effect on performance. Firmware implementations are not
always sane.

The names suggest that TRIM is for marking sectors for garbage collection while
SECURITY ERASE tries a bit harder. From the runtime performance point of view, I
would expect that S.E. is at least as fast as TRIM as no more garbage needs to
be collected at a later point. From a durability PoV, not so sure, it could be
that S.E. overwrites all blocks (or not).

Anyway, I have not read into the details and unless the standards (and
manufacturers) can guarantee certain behavior, it will likely vary between
device models.

Thank you for your reply!

[One Thousand Gnomes]

Post by Peter Wu
The names suggest that TRIM is for marking sectors for garbage collection while
SECURITY ERASE tries a bit harder. From the runtime performance point of view, I
would expect that S.E. is at least as fast as TRIM as no more garbage needs to
be collected at a later point. From a durability PoV, not so sure, it could be
that S.E. overwrites all blocks (or not).
Anyway, I have not read into the details and unless the standards (and
manufacturers) can guarantee certain behavior, it will likely vary between
device models.

On a decent SSD security erase is almost immediate and does not need to
overwrite anything.

Alan
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