Re: fstrim and Luks / dm-raid
On Sat, Oct 05, 2019 at 06:14:24PM +0200, Pascal Hambourg wrote:
> > > Is fstrim useful in suc a case ?
> >
> > It's disabled by default, but you can enable by setting
> > "issue_discards=1" in lvm.conf, and by adding "discard" option to your
> > crypttab. There's no SSD-specific mdraid configuration.
>
> Actually there is. mdraid and dm-raid have discard disabled by default
> with RAID4/5/6 for safety reasons. One must pass the parameter
> devices_handle_discard_safely=Y to the module raid456 or dm-raid
> respectively to enable it.
Curious. I avoid RAID5/6 due to the old habit, but it's something that's
good to go.
> > > Should I add the discard option in fstab ?
> >
> > It's safe only if your SSD firmware is sane and does not corrupt your
> > data while processing TRIM with NCQ enabled.
> > For instance, some noname Chinese SSD (ADATA, for instance) can corrupt
> > your filesystem in such circumstances, Samsung 850 PRO should not.
> > Manual fstrim invocation seems to be safe.
>
> Why should fstrim be safer that the discard mount option ? AFAIK they
> use the same TRIM command.
The way I heard it, to trigger the corruption one should issue TRIM
asynchronously *and* utilize NCQ for it. fstrim is synchronous.
Reco
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