Hi friends,

I got some problems in setting up a 200G hard disk in an external usb enclosure, mainly it is recognized as 137.4GB by fdisk while other things seems to work till now. I tried hard to figure it out and not very successful so far and would like to have your input.

It is a bit lengthy but I try to be organized and clear.

OS:
Redhat Linux 9.0 kernel 2.4.20-31.9smp, kernal recompiled but not much changed to default
with CONFIG_USB_STORAGE=m and all CONFIG_USB_STORAGE_*=y

HD:
7200rpm Western Digital Caviar SE WD2000 EIDE (24321c x 255h x 63s)

USB enclosures:
I have two, both Bytecc ME-720U Ali chipset, an old one claims to support more than 200G (250G?). The other new one support 300G.

When I connect the WD 200G as internal, everything works fine. And I have a Maxtor 80G in the old Bytecc enclosure and it was working so the OS should support USB external hard disk so far. The problem comes when I try to install the WD 200G to the new Bytecc enclosure. It was not recognized by /sbin/fdisk at the beginning or gave some cylinder numbering problem. I tried somehow and find out if I use the old usb enclosure for 200G and new one for 80G both can be recognized under windows xp so I stick to this configuration.

The size of the 200G was not correct when in the usb enclosure so I partitioned 3 equal partitions (8107cylinders each partition) when it is connected as internal, one (1) as ext3, two(2,3) as vfat 32bit. mkfs works fine. And it looks good under windows xp using parition magic v8.0. The two vfat partitions can be recognized under windows xp.

Now under linux, command p after "/sbin/fdisk /dev/sdb" gives:

Disk /dev/sdb: 137.4 GB, 137438952960 bytes
255 heads, 63 sectors/track, 16709 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdb1 1 8107 65119446 83 Linux
/dev/sdb2 8108 16214 65119477+ c Win95 FAT32 (LBA)
/dev/sdb3 16215 24321 65119477+ c Win95 FAT32 (LBA)

Notice the 137.4GB there, which is not the sum of sizes of any two partitions.

I can mount all the partitions and copy files to them seems working so far excepting a failure to copy a big movie file (~700M) to /dev/sdb2

The other problem is that the speed of the hard disk is quite slow, hdparm -t /dev/sdb1 gives
only 2.36 MB/s while when it was connected as internal, it gives 53MB/s, and the maxtor 80G 5400rpm gives average 24MB/s in the usb enclosure.

looking into the /var/log/message I found the following when I plug the usb line into the pc

Dec 1 01:22:15 zhejiang kernel: Attached scsi removable disk sda at scsi0, channel 0, id 0, lun 0
Dec 1 01:22:15 zhejiang kernel: Attached scsi disk sdb at scsi1, channel 0, id 0, lun 0
Dec 1 01:22:15 zhejiang kernel: sda : READ CAPACITY failed.
Dec 1 01:22:15 zhejiang kernel: sda : status = 1, message = 00, host = 0, driver = 08
Dec 1 01:22:15 zhejiang kernel: Current sd00:00: sense key Not Ready
Dec 1 01:22:15 zhejiang kernel: Additional sense indicates Medium not present
Dec 1 01:22:15 zhejiang kernel: sda : block size assumed to be 512 bytes, disk size 1GB.
Dec 1 01:22:15 zhejiang kernel: sda: I/O error: dev 08:00, sector 0
Dec 1 01:22:15 zhejiang kernel: I/O error: dev 08:00, sector 0
Dec 1 01:22:15 zhejiang kernel: unable to read partition table
Dec 1 01:22:15 zhejiang kernel: SCSI device sdb: 268435455 512-byte hdwr sectors (137439 MB)
Dec 1 01:22:15 zhejiang kernel: sdb: sdb1 sdb2 sdb3

And there is numerous repetitive error for sda

Dec 1 01:35:15 zhejiang kernel: sda : READ CAPACITY failed.
Dec 1 01:35:15 zhejiang kernel: sda : status = 1, message = 00, host = 0, driver = 08
Dec 1 01:35:15 zhejiang kernel: Current sd00:00: sense key Not Ready
Dec 1 01:35:15 zhejiang kernel: Additional sense indicates Medium not present
Dec 1 01:35:15 zhejiang kernel: sda : block size assumed to be 512 bytes, disk size 1GB.
Dec 1 01:35:15 zhejiang kernel: sda: Write Protect is off
Dec 1 01:35:15 zhejiang kernel: sda: I/O error: dev 08:00, sector 0
Dec 1 01:35:15 zhejiang kernel: I/O error: dev 08:00, sector 0
Dec 1 01:35:15 zhejiang kernel: unable to read partition table

I spent three nights on this stupid problem and was driven mad after numerous searches on google and assemble/dissemble hardware.

Please give me some advice.