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Old 12-25-2007, 07:04 PM   #1
jfxg
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partitions above 15


I have looked and can't find much on the max number of partitions that are allowed on a drive. the following Wiki is all so far that I have found and it sounds like there's no limit.
http://en.wikipedia.org/wiki/Extended_Boot_Record

I have a multi boot machine and from XP using partition magic created a partition 16 on my f disk and formated it to ext3.

I was unable to install vector linux so came up in PCLinux and with gparted tried to format sdf16 to ext3. The following is the error I got and some stats.

GParted 0.3.3

Libparted 1.8.7


Format /dev/sdf16 as ext3 00:03 ( ERROR )

calibrate /dev/sdf16 00:01 ( SUCCES )

path: /dev/sdf16
start: 194097393
end: 236043044
size: 41945652 (20.00 GiB)
set partitiontype on /dev/sdf16 00:02 ( SUCCES )

new partitiontype: ext3
create new ext3 filesystem 00:00 ( ERROR )

mkfs.ext3 /dev/sdf16

mke2fs 1.40.2 (12-Jul-2007)
Could not stat /dev/sdf16 --- No such file or directory

The device apparently does not exist; did you specify it correctly?

libparted messages ( INFO )

Error informing the kernel about modifications to partition /dev/sdf16
-- Invalid argument. This means Linux won't know about any changes you made
to /dev/sdf16 until you reboot -- so you shouldn't mount it or use it in any
way before rebooting.
The kernel was unable to re-read the partition table on /dev/sdf
(Device or resource busy). This means Linux won't know anything about the
modifications you made until you reboot. You should reboot your computer
before doing anything with /dev/sdf.



[root@localhost ~]# fdisk -l /dev/sdf

Disk /dev/sdf: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sdf1 1 12 96358+ 83 Linux
/dev/sdf2 * 13 266 2040255 83 Linux
/dev/sdf3 267 14693 115884877+ 5 Extended
/dev/sdf5 267 520 2040223+ 82 Linux swap / Solaris
/dev/sdf6 521 1284 6136798+ 83 Linux
/dev/sdf7 1285 1411 1020096 83 Linux
/dev/sdf8 1412 1538 1020096 83 Linux
/dev/sdf9 1539 1792 2040223+ 83 Linux
/dev/sdf10 1793 4403 20972826 83 Linux
/dev/sdf11 4404 7014 20972826 83 Linux
/dev/sdf12 7015 7026 96358+ 83 Linux
/dev/sdf13 7027 9458 19535008+ 83 Linux
/dev/sdf14 9459 9471 104391 83 Linux
/dev/sdf15 9472 12082 20972826 83 Linux
/dev/sdf16 12083 14693 20972826 83 Linux


[root@localhost ~]# ls -la /dev/sdf*
brw-rw---- 1 root disk 8, 80 Dec 25 18:37 /dev/sdf
brw-rw---- 1 root disk 8, 81 Dec 25 18:39 /dev/sdf1
brw-rw---- 1 root disk 8, 90 Dec 25 18:39 /dev/sdf10
brw-rw---- 1 root disk 8, 91 Dec 25 18:39 /dev/sdf11
brw-rw---- 1 root disk 8, 92 Dec 25 18:39 /dev/sdf12
brw-rw---- 1 root disk 8, 93 Dec 25 18:39 /dev/sdf13
brw-rw---- 1 root disk 8, 94 Dec 25 18:39 /dev/sdf14
brw-rw---- 1 root disk 8, 95 Dec 25 18:39 /dev/sdf15
brw-rw---- 1 root disk 8, 82 Dec 25 13:32 /dev/sdf2
brw-rw---- 1 root disk 8, 83 Dec 25 18:39 /dev/sdf3
brw-rw---- 1 root disk 8, 85 Dec 25 18:39 /dev/sdf5
brw-rw---- 1 root disk 8, 86 Dec 25 18:32 /dev/sdf6
brw-rw---- 1 root disk 8, 87 Dec 25 18:32 /dev/sdf7
brw-rw---- 1 root disk 8, 88 Dec 25 18:32 /dev/sdf8
brw-rw---- 1 root disk 8, 89 Dec 25 18:32 /dev/sdf9


I have tried this from slackware 12.0 using mkfs.ext3, I also created dev/sdf16 with mknod and had no joy. I have to assume the 15 is the max partition so my question is does any one know a way around this other than LVM.
thanks

Last edited by jfxg; 12-25-2007 at 07:05 PM.
 
Old 12-25-2007, 07:50 PM   #2
bigrigdriver
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This thread explains it: http://www.linuxformat.co.uk/index.p...ewtopic&t=6868.
 
Old 12-25-2007, 08:00 PM   #3
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I have a 254 partition limit using Bootitng. All partitions can be on one drive or spread into 8 drives, only four per drive can be configured to be seen by an OS as all partitions are primaries.
 
Old 12-25-2007, 08:17 PM   #4
jfxg
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thanks for the help. I guess I'll move everything to LVM.
I use bootitng but don't want to let it manage partitions. It seems like one more thing to go wrong.
 
Old 12-25-2007, 08:33 PM   #5
saikee
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Linux kernels newer than 2.6.20 will be using libATA drivers for detecting all Pata/Sata/SCSI/USB disks.

This decision effectively terminated the previously supported 63 partitions possible with Pata/IDE disks.

Some new kernels may be made to accept existing 15+ partitions but the trend is go with the maximum 15 partitions as established for the SCSI/Sata/USB disks.

One can use an older kernel to create 63 partitions or employ a proprietary software (hard disk management layer) to create more partitions but the modern kernels will not support them and if they are forced to use the disk the kernel will treat it as a raw disk. I have already found this out.

New kernel can only guarantee the integrity of the filing systems if there are no more than 16 disks each have no more than 16 device names. The whole of the hard disk like sda takes away one device name and that is why we can have only 15 partitions. The 16 devices times 16 disks give the 256 combinations.

All the 16 devices names in all the 16 disks are already pre-assigned with major and minor numbers. That is the Linux standard guaranteeing every device within this standard can be "mounted". Users deviating from the standard do so at their own risk.

One can check from the /dev directory after booting up the Linux. The detectable devices are all there.

LVM is a way out but not every installer supports it.
 
Old 12-25-2007, 09:09 PM   #6
syg00
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I've not been bitten by this, as I tend not be be as extreme as some with the partitions ...
I have always been averse to LVM as I move a lot of systems (and/or disks) around. So far I have managed to stay "alive".

As an aside, don't try selecting both in a kernel config. I did (accidentally) over the weekend, and a system with one IDE and one S-ATA drive came up with 3 disks.
Mmmm - well, *didn't* come up actually.
I'd reckon it's a problem with the init scripts, but I didn't really chase it.
 
Old 12-26-2007, 09:21 AM   #7
jfxg
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thanks for the help. I have two large drives that are reserved for Linux. I like to download new distributions from Distro Watch and look at them. I guess I'll have to give some thought to disk layout instead of just grabbing space at the end.
thanks for the detailed information, I like to know why I am doing something. I'm just getting into kernel customizing so it gives me something to be aware of.
Thanks again.
 
Old 12-26-2007, 11:15 AM   #8
saikee
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If you have a large hard disk you can get 44 logical partitions out of it by cheating a little bit, with the help from Grub.

I am running one myself.

Basically you use the first primary slot as an extended partition and create 11 logical partitions inside. Do whatever you want in the 11 logical partitions.

You then hide the first partition and repeat the same for the second primary slot.

4 primary slots in the partition table give you 4x11 logical partitions.

When you want to use any logical partition you hide the other 3 extened partitions and unhide the one you want access.

The disadvantage is you can access to only 11 out of the 44 logical partition at a time.

The total of partitions to the kernel is 15 at any one time; 3 hidden primaries, one unhidden extended partition and 11 logicals. Each hidden primary becomes an extended partition if unhidden.

Not much to it but it has been working for a few years for me. You also need to use this technique if you want to run Solaris and BSD in the same disk because their structure is similar to an extended partition causing error messages. The errors can be avoided if the unused ones are hidden.
 
Old 12-26-2007, 04:12 PM   #9
jfxg
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I thought about it and then looked at the GRUB manual. It's an elegant solution.
Thank you
 
Old 12-26-2007, 07:25 PM   #10
saikee
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In case if you are not clear but want to try the 44 partitions I have to state that the controlling Grub needs to be in a partition where it cannot be hidden. This is to say Grub cannot be inside any of the 44 partitions. You need to put it in another disk.
 
Old 12-27-2007, 05:04 AM   #11
jlinkels
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Just as a matter of interest: why would someone want to have that many partitions?

jlinkels
 
Old 12-27-2007, 06:02 AM   #12
saikee
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Hard disks have become affordable in recent years and more Linux distros have also flourished. A 10Gb partition is big enough to house a Linux and so a 500Gb disk can take 50 distros without trouble.

There are PC users learning Linux and one of the ways is to expose oneself to as many Linux as possible.

Booting in Linux is also simple and easy thus anybody can run as many Linux as one wishes. Booting the second Linux is identical to boot the next 200 Linux. Unless one makes use partitions one will not know Linux can be installed and booted from 63th partition at the end of a 500Gb hard disk or this partition is mountable in a MS Windows.

I still run a box with older Linux where 63 partitions are supported in a Pata disk. The 3 Pata and 2 Sata disks offer 200+ partitions and I can conduct various experiments with this box. One of the experiements I did was to write a script to make a Vista booting 150+ Linux there.

The current kernel supports 256 block devices comprised of 16 disks each with 16 device names (whole disk name + 15 partitions). Thus technically one can have 256- 16 whole disk names-16 extended partitions = 224 primary and logical partitions usable for storing operating systems.

Despite using many partitions there is a lot I do not know about partitions as the kernel has apparently widened the 16 bits to 32, (dev_t type in the kernel has been 32 bits wide for a long time. It used to be only 16 bits wide, 8 for the major, 8 for the minor).
 
Old 12-27-2007, 12:18 PM   #13
jlinkels
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Saikee, I am not sure I fully agree with you whether it is beneficial to install that many Linux distros. But I found your article on the justlinux.com forum very interesting and it was well worth reading. Thanks

jlinkels
 
Old 12-27-2007, 01:02 PM   #14
jfxg
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With SATA II's at a little over $100 for 500GB and being able to download a DVD at just over an hour I can look at what other distro's are doing. I'm learning Linux so its good to see what is possible, besides it's better than some things I could be doing.
 
  


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