Nobody has answered yet (too bad for me), but I came to the conclusion that I should accept parted suggestion instead of linux indication. Some extractions from the parted manual:
1.- Grub automatically uses LBA if it is available.
2.- LBA solves all CHS problems. However there is no reliable way for Linux or Parted to know that you're using LBA, so parted may give you warnings about cylinders not being aligned, or the BIOS geometry being inconsistent, etc. You can ignore this messages if you're using LBA mode.
3.- When your disk is in LBA mode, Parted (and most other programs) will say your CHS geometry is */255/63 - unless you switched from CHS to LBA.
Now parted warning includes:
GNU Parted suspects the real geometry should be 4864/255/63 (not 77520/16/63).
So it might be that it's under LBA mode since the geometry parted detected is */255/63 and I'm using grub as the boot loader, which tries to use LBA mode when available. However I'm not really sure about being under LBA mode, so hdparm cen provide more information:
It says LBA=yes, so I interpret this as I'm running under LBA mode (I still don't know for sure since LBA=yes might mean the BIOS accepts LBA mode, but still not being under it, notice it also provides the linux CSH, which is the one parted detects as wrong). Although I'm still not certain everything points to being under LBA mode, and therefore I just can ignore the geometry inconsitency...
I'll use parted ignoring the warnings believing that's OK, but if any one thinks otherwise, please let me know.
Sorry I didn't answer earlier - I come here once a week, usually on the weekends.
A disk's geometry, more by virtue of history than current construction, is described by the ordered triplet (Cylinders, heads, sectors). Your disk most likely has a geometry of 77,520 cylinders, 16 heads, and 63 sectors per track as seen by the BIOS.
You probably do have LBA turned on. LBA remaps this "physical" geometry to an equivalent logical geometry by increasing the number of heads and decreasing the number of cylinders. It uses the extra heads as a cylinder offset to add to the desired cylinder.
LBA isn't necessary for Linux. It was a kluge as disks grew beyond DOS's 1024 cylinder limit. The capability is still there and is used by older Windows systems that have higher cylinder limits, but still can't handle today's disks. This issue can be confusing because a controller using LBA will report one thing but a direct query of the disk will report another. This is why parted is giving you the message it does. It sounds like Linux is not really using LBA. Linux has no need of LBA because it can handle the larger values directly (and to my knowledge so does XP, but take the XP statement with a grain of salt).
BTW, modern disks no longer use the relatively simple physical geometry of (cylinders, heads, sectors) either. It produces very high areal bit densities near the center of a platter but lesser densities at the outer edge. At the very least, modern disk controllers divide the platter into rings, or zones, and use different sectors per track in different zones to keep areal densities close to the same high figure. This approach maximizes disk capacity. However, operating systems and BIOSes are all built around the old physical geometry where cylinders, heads, and sectors per track were assumed to be constant. The disk controller translates to the BIOS-driven understanding of geometry from the more complex true physical geometry.
As a matter of general principle most Linux gurus recommend not using LBA as it forces two translations - from physical to logical and logical to kludge, and so I do not use it. Next time you set up your disk, turn it off, then make sure you can boot into all your operating systems. Chances are you will be able to. If so, then leave it off.
If you are interested, you can find out more at http://www.pcguide.com/ref/hdd/geom/geom.htm. Check out that page and the hyperlink at the bottom of it to the page labeled "Physical Geometry."
jevv
3 Posts
0
April 22nd, 2004 00:00
Javier.
jevv
3 Posts
0
April 23rd, 2004 21:00
Nobody has answered yet (too bad for me), but I came to the conclusion that I should accept parted suggestion instead of linux indication. Some extractions from the parted manual:
1.- Grub automatically uses LBA if it is available.
2.- LBA solves all CHS problems. However there is no reliable way for Linux or Parted to know that you're using LBA, so parted may give you warnings about cylinders not being aligned, or the BIOS geometry being inconsistent, etc. You can ignore this messages if you're using LBA mode.
3.- When your disk is in LBA mode, Parted (and most other programs) will say your CHS geometry is */255/63 - unless you switched from CHS to LBA.
Now parted warning includes:
GNU Parted suspects the real geometry should be 4864/255/63 (not 77520/16/63).
So it might be that it's under LBA mode since the geometry parted detected is */255/63 and I'm using grub as the boot loader, which tries to use LBA mode when available. However I'm not really sure about being under LBA mode, so hdparm cen provide more information:
hdparm -i /dev/hda
/dev/hda:
...
CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=78140160
...
It says LBA=yes, so I interpret this as I'm running under LBA mode (I still don't know for sure since LBA=yes might mean the BIOS accepts LBA mode, but still not being under it, notice it also provides the linux CSH, which is the one parted detects as wrong). Although I'm still not certain everything points to being under LBA mode, and therefore I just can ignore the geometry inconsitency...
I'll use parted ignoring the warnings believing that's OK, but if any one thinks otherwise, please let me know.
Thanks,
Javier.
dacap
41 Posts
0
April 24th, 2004 19:00
Sorry I didn't answer earlier - I come here once a week, usually on the weekends.
A disk's geometry, more by virtue of history than current construction, is described by the ordered triplet (Cylinders, heads, sectors). Your disk most likely has a geometry of 77,520 cylinders, 16 heads, and 63 sectors per track as seen by the BIOS.
You probably do have LBA turned on. LBA remaps this "physical" geometry to an equivalent logical geometry by increasing the number of heads and decreasing the number of cylinders. It uses the extra heads as a cylinder offset to add to the desired cylinder.
LBA isn't necessary for Linux. It was a kluge as disks grew beyond DOS's 1024 cylinder limit. The capability is still there and is used by older Windows systems that have higher cylinder limits, but still can't handle today's disks. This issue can be confusing because a controller using LBA will report one thing but a direct query of the disk will report another. This is why parted is giving you the message it does. It sounds like Linux is not really using LBA. Linux has no need of LBA because it can handle the larger values directly (and to my knowledge so does XP, but take the XP statement with a grain of salt).
BTW, modern disks no longer use the relatively simple physical geometry of (cylinders, heads, sectors) either. It produces very high areal bit densities near the center of a platter but lesser densities at the outer edge. At the very least, modern disk controllers divide the platter into rings, or zones, and use different sectors per track in different zones to keep areal densities close to the same high figure. This approach maximizes disk capacity. However, operating systems and BIOSes are all built around the old physical geometry where cylinders, heads, and sectors per track were assumed to be constant. The disk controller translates to the BIOS-driven understanding of geometry from the more complex true physical geometry.
As a matter of general principle most Linux gurus recommend not using LBA as it forces two translations - from physical to logical and logical to kludge, and so I do not use it. Next time you set up your disk, turn it off, then make sure you can boot into all your operating systems. Chances are you will be able to. If so, then leave it off.
If you are interested, you can find out more at http://www.pcguide.com/ref/hdd/geom/geom.htm. Check out that page and the hyperlink at the bottom of it to the page labeled "Physical Geometry."