Mirroring Not Preserved Booting from Replacement Drive

ID: Q98519

SUMMARY

After a hard disk drive (HDD) crash in a system configured with a LAN Manager 2.1 server with one IDE controller, two HDDs, and fault tolerance installed with mirroring of the primary partition, you cannot bring the system back up on the replacement drive with mirroring preserved. This article explains how to make the mirror of the boot volume bootable, then explains mirroring and its restrictions.

The last section gives a brief history of LAN Manager fault tolerance.

MORE INFORMATION

The system is not designed to preserve mirroring in such situations. FTBOOT changes the partition that was the boot volume's mirror into a bootable partition, then uses the disk that contains the boot volume's mirror to boot the system.

After running FTBOOT to make the mirror of the boot volume bootable, you should:

Boot from what used to be the mirror of the boot volume.

Run FTADMIN to correct errors.

Install a new drive where the mirror of the boot volume used to be.

Run FTSETUP to mirror the boot volume and any other drives.

Reboot to let FTSETUP finish mirroring.

The first HDD cannot contain virtual drives and must be at least one MB smaller than the second HDD; the second HDD has to be at least as large as the first drive and may not be partitioned when mirroring the boot partition.

The first drive can be smaller, larger, or equal to the second drive. If the first drive is larger or the same size as the second, then the partition created on it must be 1 MB (or so) smaller than the second drive. Remember: you are mirroring partitions, not drives. So, for example, if both drives are 500 MB and the boot partition is 150 MB, then you can mirror it with no problem. You can also create another partition on drive 1 (or 2) and mirror it on drive 2 (or 1). Only as you run out of space do you start to miss the cylinder from the empty primary partition boot record on the second drive.

If both drives are 50 MB and you want to create the largest possible boot partition that can be mirrored, then you have to account for the one cylinder from the empty primary partition boot record on drive 2. The largest boot partition you can create and mirror is 49 MB.

The "1 MB smaller" restriction guarantees enough room to mirror the boot partition. FT mirrors only on secondary partitions and always retains a primary partition boot record on the disk, occupying one cylinder of space. Without a primary partition boot record, the disk would look invalid to all existing disk driver code (including BIOS ROM boot code). When you set up a drive with just one primary partition, FT does not create a secondary partition boot record, and this gives you an extra cylinder of disk space. The "one MB smaller" restriction compensates for this one cylinder difference. After FTBOOT runs, the duplicate becomes a primary partition marked as bootable. All other mirror partitions are changed to regular HPFS partitions, because the drive numbering in the FTCFG.DRV and FTCFG.SYS files is now invalid. FTBOOT doesn't mount mirror partitions, so it can't access these files to change the numbers.

The FT system in LAN Manager 2.1a relaxes some of the restrictions for setting up and recovering the boot partition.

A Short History of FT

2.0 - First revision of FT only allows "format mirror" capability. This of course excludes mirroring the boot partition.

2.1 - "Copy mirror" option added. This allows mirroring of the boot partition. To recover boot partition, no other partitions can be on the drive containing the boot partition's mirror.


         Allowed        Not Allowed
      ------   ------     ------    ------
      | C: |   | C' |     | C: |    | C' |
      ------   ------     ------    ------
      | D: |   |    |     | D: |    | E: |
      ------   ------     ------    ------

2.1a - Bug fix allows mirroring of drives greater than 1 GB. Previously you could "format mirror" a partition greater than 1 GB, but you could not verify it or correct errors via FTADMIN.

FTBOOT was also modified for 2.1a to relax the contraints on mirroring the boot drive. Now the restriction is that the boot partition's mirror must be the first partition on its drive. ("Not Allowed" above is now also allowed.)

2.2 - Bug fix to FTBOOT.

Additional query words: 2.00 2.0 2.10 2.1 2.10a 2.1a 2.20 2.2 ftboot ft

Keywords : kbnetwork
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