[zfs-discuss] zfs and fstrim

Gordan Bobic gordan.bobic at gmail.com
Thu Jan 21 03:45:13 EST 2016


What will happen to your SSDs? Nothing Unless they are truly ancient (by generation rather than age), you are unlikely to notice any difference.

Technology has long ago moved on to the point where this is not an issue worth worrying about, let alone worth agonizing about.
On 21 Jan 2016 6:11 am, John Covici via zfs-discuss <zfs-discuss at list.zfsonlinux.org> wrote:
>
> So, what will happen to my ssds?  When I had ext4filesystems, I could
> use fstrim and it would work, although I was advised that I should not
> use it too often because I might get silent bit corruption and this is
> why I wantedto use a file system which had checksums to  protect against
> the silentbitrot.  So,do Ihave tonot use zfson the ssd drives?
>
> Walter Parker <walterp at gmail.com> wrote:
>
> > fstrim requires that the File System support discard/trim before it will do
> > anything. Until ZFS on Linux supports TRIM/discard, fstrim will be a no-op.
> > It is the file system that tells fstrim/the SSD what block are now empty
> > (and can be removed from the SSD's list of blocks in use). Without writing
> > an application that parses the ZFS used/free list and then calls proper
> > APIs to mark those blocks as free, there is nothing you do to free/trim a
> > ZFS pool.
> > 
> > 
> > Walter
> > 
> > On Wed, Jan 20, 2016 at 6:16 PM, John Covici via zfs-discuss <
> > zfs-discuss at list.zfsonlinux.org> wrote:
> > 
> > > But my original question was how to use the fstrim command in a zfs
> > > pool, since I know that trim is not supported yet.  Do I use the pool
> > > name, each dataset name, or what?
> > >
> > > Thanks.
> > >
> > > fermulator via zfs-discuss <zfs-discuss at list.zfsonlinux.org> wrote:
> > >
> > > > Official information is here:
> > > http://open-zfs.org/wiki/Features#TRIM_Support
> > > >
> > > > For an elaboration into Gordan's option 2) there are numerous articles
> > > > online on how to do it; some examples, see
> > > >  -
> > > >
> > > http://techgage.com/article/enabling_and_testing_ssd_trim_support_under_linux/
> > > >  -
> > > >
> > > http://blog.neutrino.es/2013/howto-properly-activate-trim-for-your-ssd-on-linux-fstrim-lvm-and-dmcrypt/
> > > >
> > > >
> > > >
> > > > -------- Original Message --------
> > > > From: Gordan Bobic via zfs-discuss <zfs-discuss at list.zfsonlinux.org>
> > > > Sent: 1/20/2016, 9:41:18 AM
> > > > To: General discussion - ask questions, receive answers and advice
> > > > from other ZFS users <zfs-discuss at list.zfsonlinux.org>
> > > > Cc:
> > > > Subject: Re: [zfs-discuss] zfs and fstrim
> > > >
> > > > > There are a few options:
> > > > >
> > > > > 1.1) You don't
> > > > > 1.2) Leave untouched partition/space on a freshly secure-erased SSD
> > > > > so that the SSD has more known untouched blocks to work with
> > > > > (under-provisioning), and you don't worry about TRIM-ing.
> > > > >
> > > > > 2) Drop the SSD out of the array (make sure your redundancy is up to
> > > > > the task), ATA secure erase it, re-add it, resilver. Space that
> > > > > isn't used will be freshly trimmed. Repeat for all SSDs in the pool.
> > > > >
> > > > > In most cases 1.1) is good enough as SSDs are internally adequately
> > > > > overprovisioned to handle this reasonably well, especially ones
> > > > > based on Sandforce controllers that internally compress and dedupe
> > > > > the data.
> > > > >
> > > > >
> > > > > On Wed, Jan 20, 2016 at 2:17 PM, John Covici via zfs-discuss
> > > > > <zfs-discuss at list.zfsonlinux.org
> > > > > <mailto:zfs-discuss at list.zfsonlinux.org>> wrote:
> > > > >
> > > > >     Hi.  Since zfs does not support fstrim, how should I trim my
> > > pool?  I
> > > > >     have a pool with a number of datasets as  legacy mountpoints on 2
> > > ssd
> > > > >     drives -- so do I do each one separately, or how to do this
> > > properly?
> > > > >
> > > > >     Thanks in advance for any suggestions.
> > > > >
> > > > >     --
> > > > >     Your life is like a penny.  You're going to lose it. The question
> > > is:
> > > > >     How do
> > > > >     you spend it?
> > > > >
> > > > >              John Covici
> > > > >     covici at ccs.covici.com <mailto:covici at ccs.covici.com>
> > > > >     _______________________________________________
> > > > >     zfs-discuss mailing list
> > > > >     zfs-discuss at list.zfsonlinux.org
> > > > >     <mailto:zfs-discuss at list.zfsonlinux.org>
> > > > >     http://list.zfsonlinux.org/cgi-bin/mailman/listinfo/zfs-discuss
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > _______________________________________________
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> > > >
> > > >
> > > > ----------------------------------------------------
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> > >
> > > --
> > > Your life is like a penny.  You're going to lose it.  The question is:
> > > How do
> > > you spend it?
> > >
> > >          John Covici
> > >          covici at ccs.covici.com
> > > _______________________________________________
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> > > zfs-discuss at list.zfsonlinux.org
> > > http://list.zfsonlinux.org/cgi-bin/mailman/listinfo/zfs-discuss
> > >
> > 
> > 
> > 
> > -- 
> > The greatest dangers to liberty lurk in insidious encroachment by men of
> > zeal, well-meaning but without understanding.   -- Justice Louis D. Brandeis
> > 
> > ----------------------------------------------------
> > Alternatives:
> > 
> > ----------------------------------------------------
>
> -- 
> Your life is like a penny.  You're going to lose it.  The question is:
> How do
> you spend it?
>
>          John Covici
>          covici at ccs.covici.com
> _______________________________________________
> zfs-discuss mailing list
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