fdisk showing "begin" different from "start"

fdisk showing "begin" different from "start"

Post by George Brewste » Sun, 21 Dec 1997 04:00:00



I'm sure this is a very dumb question, but I didn't see the answer
anywhere in the doc and don't have a web browser running reliably now,
so I can't check dejanews. But when I run fdisk -l, it shows the
following [warinings about > 1024 cylinders cut]:

Disk /dev/hda: 16 heads, 63 sectors, 3893 cylinders
Units = cylinders of 1008 * 512 bytes

   Device Boot   Begin    Start      End   Blocks   Id  System
/dev/hda1            1        1      776   391072+  83  Linux native
/dev/hda2          777      777     2402   819504   83  Linux native
/dev/hda3         2048     2403     2443    20664   82  Linux swap

Disk /dev/hdb: 16 heads, 63 sectors, 1240 cylinders
Units = cylinders of 1008 * 512 bytes

   Device Boot   Begin    Start      End   Blocks   Id  System
/dev/hdb1            1        1     1178   593680+  83  Linux native
/dev/hdb2         1024     1179     1240    31248   82  Linux swap

What confuses me is that the "begin" and "start" fields differ on some
partitions. So I'm sure there's a perfectly good reason for this, but
I'd still like to know what's going on.

Also, I should theoretically be able to change some of the partitions
on a disk with fdisk and have the data stay intact on the other
partitions, right? I do know I should backup, and I do.

Thanks,
George

 
 
 

fdisk showing "begin" different from "start"

Post by Matthew J. Franci » Mon, 22 Dec 1997 04:00:00



> I'm sure this is a very dumb question, but I didn't see the answer
> anywhere in the doc and don't have a web browser running reliably now,
> so I can't check dejanews. But when I run fdisk -l, it shows the
> following [warinings about > 1024 cylinders cut]:

> Disk /dev/hda: 16 heads, 63 sectors, 3893 cylinders
> Units = cylinders of 1008 * 512 bytes

>    Device Boot   Begin    Start      End   Blocks   Id  System
> /dev/hda1            1        1      776   391072+  83  Linux native
> /dev/hda2          777      777     2402   819504   83  Linux native
> /dev/hda3         2048     2403     2443    20664   82  Linux swap

[...]

Symptoms like this, I discovered, (on a new 4.3G disk) can happen if
you tell your BIOS that a large disk is "Large". If this is what
you've done, the proper thing, it turns out, is for it to be "LBA"
instead.

(I don't recall (offhand) seeing this documented either? If it's not,
this should really be an FAQ; most drives are big enough to hit
this these days...)

Quote:> Also, I should theoretically be able to change some of the partitions
> on a disk with fdisk and have the data stay intact on the other
> partitions, right? I do know I should backup, and I do.

Yes (provided you do it carefully), and very sensible of you, in that
order.
However, if it's as described above, you needn't bother re-partitioning.
If it _really_ bothers you, back-up, re-type and reformat the whole
lot (I'm fairly sure changing the drive type on a "live" volume must be
Not Recommended :)
Otherwise, it should be essentially harmless. Just an artifact of how
drive geometries are stored...

If, of course, you were set on testing whether your partitioning is
sane,
the thing to do (_AFTER_ backing up) would be to fill up all your
partitions, including the reserved blocks, with something
inconsequential.
If thereafter one or more filesystems is dead, you have overlap ]:)

-Matt.

 
 
 

fdisk showing "begin" different from "start"

Post by George Brewste » Mon, 22 Dec 1997 04:00:00



Quote:

> Symptoms like this, I discovered, (on a new 4.3G disk) can happen if
> you tell your BIOS that a large disk is "Large". If this is what
> you've done, the proper thing, it turns out, is for it to be "LBA"
> instead.
> [...]

Well, I don't think that could be the problem on my computer, because
I have an ancient BIOS, which knows nothing of disks with more than
1024 cylinders. It doesn't support translation. So I have to have all
my bootable partitions below the 1024th cylinder :-( Sorry I forgot to
post that in my origional post. I'm still puzzled, though...

Quote:> > Also, I should theoretically be able to change some of the partitions
> > on a disk with fdisk and have the data stay intact on the other
> > partitions, right? I do know I should backup, and I do.

> Yes (provided you do it carefully), and very sensible of you, in that
> order.
> However, if it's as described above, you needn't bother re-partitioning.
> If it _really_ bothers you, back-up, re-type and reformat the whole
> lot (I'm fairly sure changing the drive type on a "live" volume must be
> Not Recommended :)
> Otherwise, it should be essentially harmless. Just an artifact of how
> drive geometries are stored...

I didn't make this clear in my origional post either, but I wasn't
going to repartition because of the differing Begin and Start
fields. I simply wanted to enlarge my swap partition and create some
additional space in /usr.

Quote:> [...]
> -Matt.

George