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Thomas Jahns
*nix forums beginner
Joined: 20 Apr 2005
Posts: 44
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 Posted: Wed Feb 16, 2005 9:53 am Post subject:
Re: Understanding the volume header on IRIX CD images...
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"Steven J. Hill" <sjhill@realitydiluted.com> writes:
| Quote: | 1) If I look at an IRIX CD image under Linux, fdisk gives me
a message of "Note: sector size is 2048 (not 512)". Yet the
sectors displayed for the volhdr and volume are actually 512
byte blocks. What gives? Is the CD image itself written in
2048 byte sectors and not 512 byte sectors?
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The structures on an IRIX CD (EFS format) are built for 512 byte
sectors, but the actual size depends on the device read from. SCSI
CD-ROM devices usually can be switched from 2048 byte blocks to 512 byte
and back (which is what IRIX or the PROM does for EFS vs. ISO9660
CDs). This is just a representation of the data on the CD which is
physically much more complicated (lots of error-correction and other
information only the CD-ROM device cares about). From a higher level
point of view the content on a CD-ROM is just a stream of bits and the
chunks you divide said stream into is entirely up to the hardware and
software involved.
| Quote: | 2) Partition 8 which is the filesystem also displays an Id of
5 which is 'SysV'. However, it is actually an EFS filesystem.
Why is that? I would have thought the disk would have an Id
of 7 which is 'EFS'. Can someone give some information on
this discrepancy? Did images get written in both formats, or
does IRIX simply ignore the Id of the partition?
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IRIX 6.5 at least doesn't care too much (found this when I accidentally
wrote a CD with an EFS partition tagged as XFS), hickups a little but
reads an EFS partition with incorrect Id just fine.
| Quote: | 3) Here is sample output from one of my IRIX disks:
----- partitions -----
Pt# Device Info Start End Sectors Id System
8: /dev/hdc1 4 74 1148232 5 SGI sysv
9: /dev/hdc2 0 3 48736 0 SGI volhdr
11: /dev/hdc3 0 74 1196992 6 SGI volume
Why does the sum of Partitions 8 and 9 not equal the entire volume
value in Partition 11? Also, when I do a 'dd' of the disk image
the actual size of of Partition 8 is 587784192 bytes which is
1148016 sectors of 512 bytes. That doesn't match the 1148232 value
shown above. I am beginning to doubt the validity of the 'fdisk'
command under Linux when dealing with SGI disk labels. Does anyone
have some comments on this?
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The size difference is because the volhdr partition does also contain
the volume directory (into which one cannot put files like the rest of
the volhdr) which uses a few blocks. Also you might find that rounding
prevents EFS from using all blocks in the partition. But since you are
using dd, what exactly are you seeing in your shell window? Giving some
more verbose printouts and telling what you are trying to achieve could
be helpful here.
Linux fdisk certainly isn't the best program to deal with SGI partition
layout. That's for sure. It's been some time since I mastered my own
installation CDs for IRIX so unfortunately I don't remember all the details.
Thomas Jahns
--
"Computers are good at following instructions,
but not at reading your mind."
D. E. Knuth, The TeXbook, Addison-Wesley 1984, 1986, 1996, p. 9 |
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Steven J. Hill
*nix forums beginner
Joined: 27 Jun 2005
Posts: 18
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| Posted: Tue Feb 15, 2005 10:03 pm Post subject:
Understanding the volume header on IRIX CD images...
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Greetings.
Please forgive the cross-posting. I am trying to understand a few
things about the IRIX CD images.
1) If I look at an IRIX CD image under Linux, fdisk gives me
a message of "Note: sector size is 2048 (not 512)". Yet the
sectors displayed for the volhdr and volume are actually 512
byte blocks. What gives? Is the CD image itself written in
2048 byte sectors and not 512 byte sectors?
2) Partition 8 which is the filesystem also displays an Id of
5 which is 'SysV'. However, it is actually an EFS filesystem.
Why is that? I would have thought the disk would have an Id
of 7 which is 'EFS'. Can someone give some information on
this discrepancy? Did images get written in both formats, or
does IRIX simply ignore the Id of the partition?
3) Here is sample output from one of my IRIX disks:
----- partitions -----
Pt# Device Info Start End Sectors Id System
8: /dev/hdc1 4 74 1148232 5 SGI sysv
9: /dev/hdc2 0 3 48736 0 SGI volhdr
11: /dev/hdc3 0 74 1196992 6 SGI volume
Why does the sum of Partitions 8 and 9 not equal the entire volume
value in Partition 11? Also, when I do a 'dd' of the disk image
the actual size of of Partition 8 is 587784192 bytes which is
1148016 sectors of 512 bytes. That doesn't match the 1148232 value
shown above. I am beginning to doubt the validity of the 'fdisk'
command under Linux when dealing with SGI disk labels. Does anyone
have some comments on this?
Thanks in advance.
-Steve |
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