Re: How to flush cache of certain disk?
El 2010-05-06 a las 16:36 +0300, Alexander Batischev escribió:
(resending to the list)
> Hi, and thanks for response!
>
> On 6 May 2010 16:17, Camaleón wrote:
> >> On my netbook I'm using automatic USB sticks mount through udev rules,
> >> and I already used to running 'sync' command before unplugging stick, so
> >> no data will be lost. But if I have few sticks inserted and some
> >> information copying on one of them, if I run 'sync' I have to wait while
> >> copying ends, because:
> >>
> >> a) sync command drops cache on disk, but copying process fill it again;
> >> sync will work until all the caches are dropped to disks
> >
> > Dunno if this would fit your needs, but there is a "sync" option for
> > mount points you can use to ensure all removable devices (or only the
> > ones you select) get mounted with "-o sync" flag.
> >
> > But I would be a bit reluctant to use that, because as per "man mount"
> > page that flag can shorten the life of flash drive based devices with a
> > limited number of write operations.
>
> Yes, that's why all USB sticks are mounted with async option and
> that's a reason to use 'sync' before unplugging them.
O.k.
> >> b) I can't unplug stick when it stops to flash because I can't be sure
> >> that there are no more parts of cache needed to be flushed on that disk.
> >>
> >> So here is my question - how can I run sync for only one device?
> >
> > To avoid data loss you have to "umount" the device first (or just "eject"
> > if that options is available in your system). Umount/eject operation
> > should care the data is correctly stored in the media before powering off
> > or unplugging the device.
>
> Well, yes, that's right, but I don't unmount sticks by myself — udev
> does that when I unplug USB device. Let me describe how automounting
> implemented so it would be more clear to you.
>
> When I put my flash drive into USB port, udev recognizes that, checks
> drive for filesystem type, and mount it if it's FAT or NTFS. After
> that I can work with mounted stick.
Right.
> When I unplug stick, udev unmounts it from mountpoint. Pay attention
> to moment of unmount - it happens *after* unplugging, so no cache can
> be flushed as far as device is already disconnected.
>
> I though about running umount /mnt/sd[a-z] before unplugging, but then
> decided to ask for a better way. If I won't find it, umount will be
> the solution. So, any other options?
I never do that way. I always first "umount" the device and then, I
remove the stick, but not the reverse. Removable media has to be done
that way, to prevent data loss or flash drive damage, or that is what
manufacturers say :-?
Greetings,
--
Camaleón
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