SanDisk ImageMate Dual Reader

My digital camera probably works well with GPhoto, but I've
never tried it. I find it more convenient to use a Flash card
reader.The SanDisk ImageMate Dual Readers are a line of external USB
Flash card readers with two slots, able to read two different Flash
card formats. Three ImageMate Dual Reader models are available:
CompactFlash and SD/MMC card, CompactFlash and SmartMedia and
CompactFlash and Memory Stick. Only CompactFlash Type 1 is
supported.The ImageMate Dual Readers are compact, with a short USB
cable that can be stored completely inside the reader. They also
come with a USB extension cable. For typical desktop use, you
probably would use the USB extension cable. But the short cable
tucked inside the reader might be convenient when traveling with a
laptop.My ImageMate Dual Reader is an SDDR-73, with CompactFlash and
SD/MMC card slots. I got it working under Linux, and it's
unexciting--it simply works. In the rest of this article I describe
how to set up an SDDR-73, but the instructions should work equally
well for the other models.Setting Up Kernel ModulesIf you use a Linux distribution that provides a precompiled
kernel, you already may have a kernel setup that works with the
ImageMate. If so, you can skip this section. If not, read
on.You need several modules in your kernel, either compiled in
or loaded before you use the card reader. From the SCSI support
section:

• SCSI Support (CONFIG_SCSI, scsi_mod.o)
• SCSI disk support (CONFIG_BLK_DEV_SD,
  sd_mod.o)
• SCSI generic support (CONFIG_CHR_DEV_SG,
  sg.o)
• Probe all LUNs on each SCSI device
  (CONFIG_SCSI_MULTI_LUN) enabled.

from the Filesystem section:

• DOS FAT fs support (CONFIG_FAT_FS, fat.o)
• MSDOS fs support (CONFIG_MSDOS_FS, msdos.o)
• VFAT (Windows-95) fs support (CONFIG_VFAT_FS,
  vfat.o)

from the USB support section:

• Support for USB (CONFIG_USB, usbcore.o)
• USB drivers for your computer; one or more of:
  
  • ECHI HCD (CONFIG_USB_EHCI_HCD, ehci-hcd.o)
  • UHCI (CONFIG_USB_UHCI, usb-uhci.o)
  • OHCI (CONFIG_USB_OHCI, usb-ohci.o)
• USB Mass Storage support (CONFIG_USB_STORAGE,
  usb-storage.o)

Setting Up Your SystemThe ImageMate is recognized as a USB storage device. The
Linux kernel treats USB storage devices as SCSI devices, so it is
assigned a device of /dev/sdx, where
x is a letter from a to z. My system has no
SCSI devices, so the ImageMate is assigned to the first SCSI drive,
/dev/sda. But it's also to /dev/sdb, because the CompactFlash card
slot is assigned to one SCSI device, and the SD/MMC card slot is
assigned to a second.For this all to work correctly, your SCSI subsystem must have
been compiled with the option to Probe all LUNs on each SCSI device
(CONFIG_SCSI_MULTI_LUN) enabled. LUNs, or logical unit numbers, are
a way for a single device to be treated as multiple devices. If the
Probe all LUNs option is set to false, only the first slot in the
reader (the CompactFlash) will actually work.To tell which SCSI drive your ImageMate is assigned to,
simply look at your system log files. The kernel log should have
messages about this, and if you boot with the ImageMate attached,
the dmesg command also will show the information.I suggest you create abstract names for the card reader in
/dev. You should have a name for each card slot device, for
example:

# ln -s /dev/sda1 /dev/cf
# ln -s /dev/sdb1 /dev/mmc

You need to state /dev/sda1 rather than /dev/sda; otherwise,
the mount command will fail with this message:

mount: wrong fs type, bad option, bad superblock on /dev/sda,
       or too many mounted file systems

The actual problem is none of these things; it's simply that
you didn't specify which partition to mount. /dev/sda1 specifies
the first partition. (On a Flash card, there is probably only a
single partition.)Next add the following lines to your /etc/fstab file:

/dev/cf         /mnt/cf         vfat    rw,user,noauto          0 0
/dev/mmc        /mnt/mmc        vfat    rw,user,noauto          0 0

With these lines in place, you can mount a CompactFlash
with:

mount /mnt/cf

Be sure to unmount it before removing the Flash card:

umount /mnt/cf

When you add the mount points to /etc/fstab, you can mount a
Flash card easily from a GNOME 2.x desktop. Simply right-click on
the desktop, choose Disks from the menu and choose the Flash device
you wish to mount.In KDE, you need to create an icon for each of the Flash
readers' slots. Instructions on how to do this are available
here.I paid about $30 for my ImageMate, and I am very satisfied
with it. Getting it to work under Linux was easy, and it is working
well.The Care and Feeding of Flash CardsFlash cards don't last forever, but here are a few tips on
how to take care of them so they can last longer.Any given sector on a Flash chip can be written to only a
certain number of times. Although this number is quite high
(hundreds of thousands of writes, at least), some parts of the
Flash card are written to rather frequently, specifically, the file
allocation table (FAT).Most Flash cards are formatted using the FAT filesystem. The
FAT itself, where files are allocated, is written to multiple times
whenever you write or delete a file. If you delete a hundred files,
you must write to the FAT at least a hundred times. For this
reason, when I wish to wipe clean my camera's Flash cards, I
usually don't delete the files. Instead, I use the camera's Format
feature, which gets rid of all the photos with minimal writes to
the chip. (Of course, if you want or need to leave some photos in
place while deleting others, go ahead.) For the same reason, if you
have many small files you wish to save on a Flash card, it is best
to bundle them into a tar file first.If you have a device such as a camera that uses Flash cards,
you probably should use that device to format the Flash card. If
you want to format under Linux, be quite sure to use the same
format the device expects. For example, my camera expects FAT16 on
a Flash card; if I were to format it as FAT32, the card would not
work in my camera. You can use the minfo command from the MTools
package to find out how a Flash card was formatted. This command
tells you the exact mformat command line you need to use to format
another card in the same manner. If you are formatting a card
purely for use with Linux systems, you can use any legal filesystem
(such as ext2).Sometimes the Flash card may develop a bad sector. For
example, during my last vacation I discovered that my camera would
hang with one particular CompactFlash card when it was
three-quarters full. I suspected a bad sector. I formatted it under
Windows with Bad Sector Scan enabled, after which it again worked
reliably. The Linux equivalent would be to run the mbadblocks
program from the MTools package; this finds bad blocks and marks
them bad in the FAT. However, in my testing with my ImageMate, I
have found that mbadblocks hangs before completing its check of a
Flash card. I am going to contact the MTools maintainers and see if
mbadblocks can be made to work correctly. For now, assume it
doesn't work.Steve Hastings first used
UNIX on actual paper teletypes. He enjoys bicycling, music, petting
his cat and making his Linux computers do new things.

email: srhastings@langri.com