Overcome the limit to solve the new idea of installing Sco Unix on a large hard disk

Bkjia.com exclusive Article I. Question raised

The larger the hard disk, the more worried I like. 10 years ago, I encountered a problem where I did not know that the BIOS of The 586 computer had exceeded the 8.4 GB hard disk capacity, and the Windows Nt operating system did not recognize that the hard disk capacity had exceeded GB, when Linux is started through LILO, it cannot break the hard disk 8.4G capacity limit.

The main reason is that in the past, the BIOS used the 8-bit addressing mode number from 0 to 7, so the range he represents is a change between 0 and, and the hard disk capacity is calculated as follows: 512 X number of cores X number of cylinders X number of sectors per track, the size of each sector is 1024 bytes, so the maximum addressing range is: 255*512/1024*63*1024/8.4) = G.

Currently, the BIOS of the computer motherboard is generally 48-bit addressing, which has already solved the limitation of GB hard drive. Recently, our server room has been upgraded to replace old servers, and we need to replace the UNIX system with new servers, the data center has a batch of new Dell OptiplesGx755 PCs, which are configured with a GB hard disk and used as a UNIX Server. The operating system is Sco UNIX Open Server 5.0.6.

Install UNIX on it according to the default parameters. After installation, you can only find 8 GB hard disk space after entering UNIX. Because these machines are specially configured to work in UNIX, the remaining 7% GB cannot be used, and the hard disk utilization is only, which is a great waste of resources. We started our experiment and tried different ways to solve the problem.

2. Results of a group of Experiments

In order to overcome this problem, we used the replacement method for repeated experiments. on HP, IBM, and a variety of GB hard drive PCs, we adopted the large-capacity hard drive installation mode not provided by SCO, when Sco OpenServer 5.0.6 is installed with the specified parameter in biosgeom, the following conditions are found:

A) install UNIX and other normal boot on multiple PCs of IBM and HP, but the hard drive for installing OS is removed to the DELL machine, but the boot is not normal, "no OS" is displayed at startup ";

B) If gb unix is installed on a dell pc, the system cannot boot normally when you use the large hard disk installation parameters. "no OS" is displayed when you start the system. By default, only 8 GB disk space can be recognized, great Waste. Therefore, I think that Dell's Gx755 pc should be able to support Unix, otherwise 8g UNIX would not be available.

Iii. analyze the cause

Based on the above situation, I think the key problem lies in that the Main Boot Sector of the hard disk is located in the whole hard disk's 0 track, 0 cylinder, 1 sector), and further analysis, the composition of the primary Boot Sector of the hard disk is the Main Boot Record 1BEH byte) + the Partition Table 40 H byte) + the end mark 2 H byte ).

The installation program of the UNIX system writes the hard disk parameters to the Master Boot Record: When UNIX is installed for the first time, because the Master Boot Record on the original hard disk is not in UNIX format, the installer will want to write the hard disk to the Master Boot Record in UNIX format. Later, use the default parameter to reinstall UNIX. If the original Master Boot Record is already in UNIX format, the installer will not modify the Master Boot Record; if biosgeom is used to specify the parameter for installation, the UNIX installer will overwrite the Master Boot Record.

When UNIX is installed by default, the installer can recognize a maximum of 1024 Cylinder hard disks. when the actual number of Cylinder hard disks is less than 1024, the installer writes the actual Cylinder, Head, number of Sectors disk size = cylinders x heads x sectors per track x 512); when it exceeds 1024, the installer marks the hard disk's cylinder number as 1024 in the Master Boot Record, together with head, write sectors together

The Master Boot Record of the hard disk. These parameters indicate the total capacity of the hard disk, while the UNIX partition size is defined in the partition table. During UNIX boot, the number of Cylinder, Head, and Sectors displayed by the system is read from the Master Boot Record. If the number of Cylinder in the Master Boot Record exceeds 1024 during Dell P c UNIX boot, the BIOS boot program cannot find the operating system and displays "no OS ".

Iv. Solution

The hard drive controller on the market now has an address translator installed inside it, which has already exceeded the limit of 1024 cylinders. However, we should pay attention when installing the system, make sure to set the hard disk to LBA mode in BIOS. The solution is as follows: assume that on a gb unix hard disk, the Master Boot Record is replaced with the Master Boot Record of a UNIX hard disk that can boot 8 GB normally, when guiding the system, you should be able to find the operating system. As long as the machine can boot, the space that UNIX can find is determined by the partition table. Real valuable things won't easily exit the stage of history. Debug is one of these classic works, but he has to be invited out at a crucial moment.

Procedure:

(A) install a Dell Pc that can boot 8g unix;

(B) Do A dosboot U disk, with debug.exe tool, in BIOS settings first boot settings for USB-HDD mode U disk boot disk method reference other articles ).

(C) boot with a floppy disk on the Dell Pc where 8g unix is installed, go to Debug, extract the Master Boot Record of the hard disk, and save it on the USB flash disk.

-A 100 CS: 0100 mov ax 201 CS: 0103 mov X, 200 CS: 0106 mov cx, 1 CS: 0109 mov dx, 80 CS: 010C int 13 CS: 010E int 20 CS: 0110 -G = 100 -Rcx, : 1be -N A: UBOOT.8G -W 200 Writing 1be bytes -Q

D) reinstall the UNIX system. Enter defbootstr biosgeom = (15665,255, 63) after the boot command appears. During the installation process, select the entire hard disk to the UNIX system. The numbers of C ylinders, Heads, sectors-per-track, and head = 15665,255 in the above 255 and 63 indicate the LBA mode respectively.

E) The 120g unix pc is installed with a USB flash drive again, and the existing Master Boot records are replaced with the Master Boot Records extracted in step 3.

-A 100 CS: 0100 mov ax 201 CS: 0103 mov X, 200 CS: 0106 mov cx, 1 CS: 0109 mov dx, 80 CS: 010C int 13 CS: 010E int 20 CS: 0110 -G = 100 -N A: UBOOT.8G -L 200 CS: 0100 mov ax, 301 CS: 0103 -G = 100 Q

After such processing, the Dell Gx755 pc can boot 120G UNIX

V. Conclusion

(A) During system boot, the number of cylinders displayed is 1024. The experiment shows that the use is not affected;

(B ). go to the UNIX system and run the df-v command to check that the hard disk space is 110 GB. This is a normal phenomenon. The formatting capacity of the hard disk is smaller than the nominal capacity; you can also use dkinit/dev/rhd00 or rhd01) to view all the cylinder information used by the system. Hd00 represents the entire physical hard disk hd01 represents the first partition. in UNIX systems, the hard disk is a character device, so the file name starts with "r.

(C). Install UNIX using this method. The main boot sector can be extracted once and used multiple times. Is a mature and stable solution;

(D). In addition, you can remove the disk from the disk by obtaining the hard disk parameters. You can also directly use tool software such as Diskman and PowerMax to measure the value.

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