On Thursday 22 April 2010 17:50:06 Greg Freemyer wrote:
Let me know where the below should be posted if not the factory list.
It relates to how 11.3 will handle SSD discards.
There is currently a fairly large thread on the Ext4 mailing list that
I've been participating in.
The basic conclusion is that for SSD based drives that can benefit
from discards, there are two existing approaches.
One is in the current kernels and it involves invoking discard any
time data blocks are freed up. Thus it can mean large number of
discards per second. This code was written and accepted into the
kernel prior to any hardware to really test it with.
Apparently now that vendors are shipping SSDs that support discard,
that methodology is proving to be a loser and SSD performance is lower
if it is enabled, instead of higher which is the entire goal of the
discards. I haven't seen benchmarks yet for this with high-end SCSI
array backends. If they too are bad, the existing logic is very
likely to be tossed from the kernel. Not sure what will replace it in
the kernel, if anything.
Alternatively, hdparm was enhanced a year or so ago to have several
discard related functionalities. That functionality is already in
11.2 and factory, so there's no issue there.
But hdparm is only providing base functionality and it needs a script
to actually invoke it correctly and cause the appropriate sectors to
be discarded. Fortunately Mark Lord (the hdparm maintainer) is now
also including "wiper.sh" with hdparm that will scan a filesystem
(ext4 and xfs for sure and possibly others) and invoke discard in a
very efficient way.
I don't think 11.2 or factory are including that script, but I'd like
wiper.sh is included already in 11.2 :
rpm -ql hdparm | grep wiper
to see it go in as the opensuse 11.3 methodology for
on a SSD.
That will mean including the script, testing it as part of opensuse,
and getting it in the nightly cron scripts or something.
in README.wiper I see a
lot of thinks like:
This script may be EXTREMELY HAZARDOUS TO YOUR DATA.
btrfs -- DO NOT USE !!!
so creating some default crontab rule with wiper.sh for openSUSE doesn't look
safe for me ...
How does a decision like that get made, etc.
I think openFATE is good place
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