Mailinglist Archive: opensuse-factory (439 mails)

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Re: [opensuse-factory] Adding SSDs?


C <smaug42@xxxxxxxxxxxx> wrote:

On Thu, Mar 13, 2014 at 9:26 PM, Jason <relentropy@xxxxxxxxx> wrote:
As for the discard, few people have told me in the past few days not
to use it
and considering they know what they're talking about I'm not
questioning it so
I have personally removed it.

The only reason I can think of that someone would suggest not using
discard is that it can impact the speed of deleting content off the
drive. https://patrick-nagel.net/blog/archives/337

That blog post is directly on point for why I recommended fstrim over discard.

As I put in an earlier email, until recently all SSDs implemented trim as a
non-queue-able command, so every trim command triggered a internal drive cache
flush. Per that blog post that caused a 40x increase in time to delete an
unpacked kernel tree. Ie. It makes ext4 perform like xfs of 3 years ago.

Newer SSDs may have finally implemented trim as a queue-able command and thus
the cache flush is no longer done. For them discard should be a fine option,
but I've seen no benchmarks.

Unfortunately I don't know how to know which way a SSD has the trim command
implemented. Maybe do what the blog author did and test untar'ing and deleting
a kernel tarball. Be sure to include the time for sync after rm -r.

Greg
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