Why Is There a USB Partitions per Device Limit? (and other USB access questions)
I put a 80 GiB HD with 33 partitions on it into a USB 2.0 enclosure, then connected it to a SuSE 9.2 system. 13 "SuSE hardware detection" windows popped up, and the taskbar became unusable for reaching any of them, which I needed to do to find the earliest ones without moving each off the stack they created all on top of each other, and only the last could be focused anyway. Why did I get 13 and not 14? No reason for "sdb4" I know, but why was "sdb2" was omitted? I selected 4 of those partitions for opening, those which as a normal ATA HD would be hdx3 msdos, hdx5 ext2, hdx7 ext3 & hdx9 msdos. The too-long-winded device names gave me the clues to which to open, which then mounted as e.g. /media/usb-0x0402-0x5621:0:0:0p5 (in the urlbar) seemed perfectly accessible in X. What causes those long mountpoint names while the Konq "my computer" content window shows them all as sdbx? Is there some way to force the automounter's mount points to be something simple like /mnt/sdbx? What is the name of the automounter? Why didn't I get a popup window for every partition on the device (33 gross total, minus sdb4)? I know that ATA HD have a generous 63 partition limit, while SCSI is limited to 15. Why the lower limit for SCSI, and why is USB treated as though SCSI? Is there some way to access all partitions in an ATA HD like mine while connected as USB? Konq shows all the usb/scsi partitions as unmounted, but 'mount' shows all mounted except any I explictly unmounted via the command line. How in X do I actually make sure all are unmounted so that disconnecting the device is safe? How do I access these partitions without X running? IOW, when I plug in the disk, what mounts them, and how do I unmount them to remove the device? Surely running umount for each and every partition must not be the only way? Man for mount and for fstab do not list a fstype of subfs, which is what 'mount' shows for the usb partitions. What is type subfs? Why wasn't I allowed to choose which popup window I want from the KDE taskbar (focus any but the last opened popup)? What doc should I be looking for that does or should explain these things? -- "He who believes in me will live, even though he dies; and whoever lives and believes in me will never die." John 11:25 NIV Team OS/2 ** Reg. Linux User #211409 Felix Miata *** http://members.ij.net/mrmazda/
On Saturday 05 February 2005 02:51 pm, Felix Miata wrote:
Why didn't I get a popup window for every partition on the device (33 gross total, minus sdb4)? I know that ATA HD have a generous 63 partition limit, while SCSI is limited to 15. Why the lower limit for SCSI, and why is USB treated as though SCSI?
Sorry for the clipping, but there is a limit of 2 questions per posting. ;-) Just because you CAN put that many partitions on a disk does not make it wise. And when you move it from an environment where it could expect to find up to 63 partitions to one where there is a limit you suddenly realize why it is NOT wise. As to all the WHYs, thats just the way it is. That is how the drivers were written, how the products were developed and evolved over time. SCSI is probably using only a few bits to indicate the partition number, and you exceeded it. You can get the source code for any of the drivers involved and attempt to re-write it I suppose, but it might be quicker to use directories for those things you are trying to use partitions for, and get down to a reasonable number of partitions. Most hotplug devices end up getting handled by SCIS in Linux. As for your last question:
What doc should I be looking for that does or should explain these things?
You seem to want to know the reasons why Linux was developed in a certain way over the many years of its life. There may be such a book, bur I doubt it will help you get access to all your partitions. It would seem more profitable in the short run to put the drive back where it came from and re-structure the data into fewer partitions rather than starting with the history of Linux. Look into Kwickdisk or Kdiskfree. Nice GUI mounting tools. Also read the manuals that came with your Boxed set. -- _____________________________________ John Andersen
John Andersen wrote Sun, 6 Feb 2005 16:30:31 -0900:
On Saturday 05 February 2005 02:51 pm, Felix Miata wrote:
Why didn't I get a popup window for every partition on the device (33 gross total, minus sdb4)? I know that ATA HD have a generous 63 partition limit, while SCSI is limited to 15. Why the lower limit for SCSI, and why is USB treated as though SCSI?
Sorry for the clipping, but there is a limit of 2 questions per posting. ;-)
I could have written far more. The post followed my worst attempt at a SuSE install ever. If I wasn't so tired I would have, and eventually, when I can find the time, and remember it all, I need to. I confined the post to only one of several installation failure subjects.
Just because you CAN put that many partitions on a disk does not make it wise.
Sometimes just a few isn't possible. When you have upwards of 3 operating systems installed per machine, and rightly keep data segregated from OS, and from apps also as well where feasible, they can quickly multiply.
And when you move it from an environment where it could expect to find up to 63 partitions to one where there is a limit you suddenly realize why it is NOT wise.
Just a few mega partitions per device have their limitations too. I choose to keep things in more manageable smaller chunks that really have no need to grow as disk capacities continue to escalate.
As to all the WHYs, thats just the way it is. That is how the drivers were written, how the products were developed and evolved over time.
Sad that complicated and difficult as SCSI is that it had to be further complicated by co-exising USB treated as SCSI.
SCSI is probably using only a few bits to indicate the partition number, and you exceeded it. You can get the source code for any of the drivers involved and attempt to re-write it I suppose, but it might be quicker to
Driver writing is for programmers, not users. Nice as it would be if it did, open source doesn't automatically turn users like me into competent programmers.
use directories for those things you are trying to use partitions for, and get down to a reasonable number of partitions.
The number available on any particular boot is perfectly reasonable right now. Windoze or DOS get 2. OS/2 gets at least 3, keeping apps and OS separate from data, for which only one is not always reasonable. Linux gets one for /boot, one for /, one for swap, and one for /home minimum. So, there's about about 9 for a 3 OS system. Double that (minus 1 for swap) for one clone backup for each partition minimum, and the count is already well past the limit of 15, and leaves nothing for extra backups for test installs.
Most hotplug devices end up getting handled by SCIS in Linux.
No manual entry for SCSI. No manual entry for SCIS. Man entry for hotplug is only one page. It points to /usr/share/doc/packages/hotplug/README, which has a section on "storage devices" that says only "To be written by adrian".
As for your last question:
What doc should I be looking for that does or should explain these things?
You seem to want to know the reasons why Linux was developed in a certain way over the many years of its life. There may be such a book, bur I doubt it will help you get access to all your partitions.
I'm looking for some dialog as much as anything. With other distros I've used, those with open development like Fedora and Mandrake, there are forums for dialog with developers that I've yet to find with SuSE. As long as I'm not handicapped by treating an ATA HD as a SCSI device, I've no problem. As it is, pretending a USB device is a SCSI device complicates system management when the system actually has SCSI devices, which virtually all mine have. NAICT from bugzilla on Fedora and Mandrake, this pretending USB is SCSI is giving both developers extra headaches as well as giving users like me extra headaches. From what I've seen, SCSI that used to work with older distro versions and kernels commonly breaks in testing of newer releases, and tends to not get fixed before official release of the new version, leading to threads here like the current "[SLE] 9.2 scsi install: no fstab found" begun Sat, 5 Feb 2005 01:05:52 -0800. The 15 partition SCSI limit was designed long long long ago when disks were relatively infinitesimal compared to what we have now. Even though the smallest new disks provide huge capacity, the availability of such capacity in many configurations is simply gross overkill, far more than someone whose system purpose is something other than collecting as much stuff as possible. That leads to finding other uses for all that excess capacity, hence archival partition backups to so-called "convenient" USB. Backing up the huge volume of data on 60G, 80G, 120G, 160G & larger drives is no small challenge. It would be nice to see this unneeded impediment removed.
It would seem more profitable in the short run to put the drive back where it came from and re-structure the data into fewer partitions rather than starting with the history of Linux.
The device is a backup device. It's purpose is for backing up partitions, and as such, the method most easily serving the purpose is exact sector by sector cloning. A major idea behind USB is simplification, both of physical, and of logical connection, including device sharing. So, this device has partitions from multiple systems, each with multiple partitions. The artificial limitation built into SCSI is an insurmountable obstacle here, forcing me to return to opening cases, shutting down systems, plugging in internally, rebooting, etc, etc, etc.
Look into Kwickdisk or Kdiskfree. Nice GUI mounting tools. Also read the manuals that came with your Boxed set.
I hope it turns out to be a lot better than the online docs I've found so far. Used to be online docs were sufficient. It took an hour yesterday to initialize the KDE help system, and it turned up nothing of much use for USB when it finally finished. -- "He who believes in me will live, even though he dies; and whoever lives and believes in me will never die." John 11:25 NIV Team OS/2 ** Reg. Linux User #211409 Felix Miata *** http://members.ij.net/mrmazda/partitioningindex.html
participants (2)
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Felix Miata -
John Andersen