Hello Lukas! I'm really happy about your detailed comments! Thanks a lot! On Tue, 16 Oct 2012, Andreas Hartmann wrote: Lukáš Czerner wrote: > On Thu, 4 Oct 2012, Andreas Hartmann wrote: > >> Date: Thu, 4 Oct 2012 06:47:36 +0200 >> From: Andreas Hartmann <andihartmann@xxxxxxxxxxxxxxx> >> To: util-linux@xxxxxxxxxxxxxxx >> Subject: Questions concerning fstrim and online discard. >> Resent-Date: Mon, 15 Oct 2012 16:10:43 +0200 >> Resent-From: Karel Zak <kzak@xxxxxxxxxx> >> Resent-To: Lukas Czerner <lczerner@xxxxxxxxxx> >> >> Hello! >> >> Please, may I ask you some questions because I'm a little bit confused >> about the behaviour of fstrim and online discard (ext4)? >> >> >> I'm using the following configuration / partitioning with a SSD >> (Controller: SF-2281; Corsair Force GT 240GB): >> >> - dm_crypt: cryptsetup luksOpen - version 1.4.1, device-mapper >> version 1.02.75 > > Hi Andreas, > > I hope that you realize that using discard with dm_crypt is not > safe. I know about this problem. My understanding is: trim usually writes 0 to the free addresses, hence it is possible to see which addresses are used and which are unused. The SF-2281 controller seems not to write zero to the addresses, hence the problem shouldn't be with this controller? Or did I got something wrong? cat /sys/block/sda/queue/discard_zeroes_data 0 > >> - lvm version 2.02.96 >> - ext4, option discard; kernel version 3.4.11 >> >> All seems to work fine, I can't see any errors in messages or in dmesg >> according trim / discard. > > The question is what kernel version do you use ? 3.4.11 :-) > Currnently we will > ignore all errors coming from the online discard including the > situation where the device does not support discard. > > This is not exactly ideal, because we should really inform user that > there was an error. Yes, this would be really important! > However we should _NOT_ inform user about every > discard request failed with EOPNOTSUPP because we can have > multi-disk devices where some of the devices support discard and > some of the does not, this is perfectly valid situation and kernel > should not scream. Once at the moment the device is mounted would be enough. > Nevertheless I am going to change things so that we inform use about > problem (other than EOPNOTSUPP). And maybe warn once a day that > part, or whole device does not support discard at all - I think that > this should not hurt. > >> >> Now, I tested fstrim from util-linux version 2.19, and surprisingly got >> this unexpected error: >> >> fstrim: /: FITRIM ioctl failed: Operation not supported > > Actually kernel version is what matters. > >> >> Why do I get this error? Online discard always seemed to work fine (= I >> didn't get any error). > > Those errors probably got silently dropped so you did not know about > them. But if fstrim works, online discard will work, too? Or is this conclusion wrong (ext4)? [....] > I hope it helps. Yes, it really helped a lot! Kind regards, Andreas Hartmann -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
