drives. Note that Windows has no real problem (despite complaints to the
contrary) when you plug and unplug, say, a USB "pocket drive". Linux,
on the other hand, in general, does tend to have problems.
I believe this is because (and someone who knows better correct me if I
am wrong about this), in the case of the Windows USB drive, the file system
is FAT32 (or FATsomething -- maybe NTFS, but I doubt that). I suspect that
the FATxx type file systems are ones that neither benefit from, nor require
or allow memory cacheing. Changes (writes) to the file system on the
removable USB drive happen directly to that drive with no buffering.
Hence, the drive can probably be "hot removed" without incident, provided
all IO to that drive is done already.
Maybe someone else can provide some more facts / illumination here...
And by the way, yes, I have used USB memories (in my case, a CF card from my camera plugged into a USB interface device). Linux did a fine job of locating and mounting this drive (well, it's been awhile, but I think I manually mounted the drive in my case). I believe the filesystem type in that case (created by a "format" done with the CF card in the camera) was a Windows FATsomething filesystem.
I think Linux got a little upset if I unplugged the USB memory drive
without doing something to umount it explicitly first, but if I recall
correctly, it didn't have any big problems after that, and the filesystem
remained intact.
Oh, and by the way, lest you think that those pocket USB "drives" must be faster than a disk because they are just "memory", think again. They are flash memory, which turns out to be slower than a lot of disks out there, strangely enough.
K
On Wednesday, November 19, 2003, at 03:45 PM, Jason Dixon wrote:
On Wed, 2003-11-19 at 14:45, Ken Rossman wrote:I know there are plenty of folks that use removable USB flash media
and/or USB external drives, so I'm hoping someone has solved this. I'm
attempting to have automount mount a Maxtor external USB drive when
it's
plugged in, and unmounted when it's unplugged.
I'm sure someone else will give you the right answer / missing pieces
for the automount part, but if you are implying that you want the drive
to automatically be unmounted just by unplugging it, I don't think that
is possible. I believe that Linux will need the chance to write out any
memory-cached data to the drive before it "goes away" first...
Good point, duh. The reason I was asking is that I'm considering
replacing a client's tape with a swapping of external USB drives. After
further consideration, I'll just have the backup script perform the
mounting/umounting, leaving it unmounted for the rest of the time it's
unused.
P.S. Has anyone tried these "pocket" USB drives that I'm seeing? Those
would be a really nice alternative to hauling around full-size drive
enclosures.
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