Re: [gentoo-user] Testing a used hard drive to make SURE it is good.

[Rich Freeman <rich0@gentoo.org>]

On Tue, Jun 16, 2020 at 7:36 AM Michael <confabulate@kintzios.com> wrote:
>
> Just to add my 2c's before you throw that SMR away, the use case for these
> drives is to act as disk archives, rather than regular backups.  You write
> data you want to keep, once.

If your write pattern is more like a tape SMR should be ok in theory.
For example, if you wrote to a raw partition using tar (without a
filesystem) I suspect most SMR implementations (including
drive-managed) would work tolerably (a host-managed implementation
would perform identically to CMR).  Once you toss in a filesystem then
there is no guarantee that the writes will end up being sequential.

And of course the problem with these latest hidden SMR drives is that
they generally don't support TRIM, so even repeated sequential writes
can be a problem because the drive doesn't realize that after you send
block 1 you're going to send blocks 2-100k all sequentially.  If it
knew that then it would just start overwriting in place obliterating
later tracks, since they're just going to be written next anyway.
Instead this drive is going to cache every write until it can
consolidate them, which isn't terrible but it still turns every seek
into three (write buffer, read buffer, write permanent - plus updating
metadata).  If they weren't being sneaky they could have made it
drive-managed WITH TRIM so that it worked more like an SSD where you
get the best performance if the OS uses TRIM, but it can fall back if
you don't.  Sequential writes on trimmed areas for SMR should perform
identically to writes on CMR drives.


-- 
Rich