Hardware/Software Requirements for Fault Tolerance (96735)

SUMMARY

This article discusses basic requirements for fault tolerance. It also addresses specific hardware issues such as IDE drives, Micro Channel and Compaq EISA machine configurations, as well as some less common software issues such as third party .BID files, LAN Manager's Network Productivity Pack, and unique boot mirroring options.

IDE DRIVES

The system must have at least two hard drives, preferably not IDE. (IDE = integrated device electronics: a type of disk drive that does not need a separate adapter card because it has resident controller electronics.) IDE drives can hang the server if they experience a massive failure such as loss of data cable or power connection.

NO PROPRIETARY DRIVE USE

The system must not be using the drives in a proprietary manner. For example: IBM Micro Channel machines apparently place IML microcode required for booting on the boot drive. This conflicts with fault tolerance and makes it impossible to boot from the mirror of the boot drive. On these types of machines, fault tolerance seems to install and work successfully, but in the event of failure the mirror will not boot.

EISA CONFIGURATION PARTITION

Compaq's EISA machines have a special partition for storing EISA configuration information, and although fault tolerance has been successfully implemented on a Prosignia using an Adaptec 1742 controller, and the mirror made bootable with FTBOOT, this EISA configuration partition was not mirrored. Testing indicates that you can reinstall the EISA configuration partition onto the former mirror from diskette.

However, in testing with the Systempro/XL, FTSETUP's "View" option reported the status of the C: drive as "Cannot mirror" when the EISA Configuration Partition was installed. Removing this partition allowed the boot drive to be mirrored successfully.

MIRRORING DRIVE MUST BE RAW

The drive becoming the mirror must be raw (not formatted, not partitioned). In cases where setting up fault tolerance interferes with drive lettering, it often is the case that a second drive has been installed and then partitioned/formatted. If you create a primary partition on a new drive in FDISKPM, drive letters are reassigned if there are extended partitions on the other drives.

OS/2 1.3 AND LADDR

The system must be running OS/2 version 1.3 and using a LADDR disk driver either supplied with it or by a third party source. HPFS must be on the partition to be mirrored (FAT drives can be selected for mirroring but the process reformats them to HPFS). The partition(s) to be mirrored/duplexed must not take 100 percent of the drive. For smaller drives, 2 MB of leftover unpartitioned space may be enough. For larger drives, 2 to 5 percent free space would be a better amount to use. OS/2 installation does not prompt for a partition size if the disk is already partitioned, so if a disk's partition already uses 100 percent of its capacity you must either delete the partition or repartition the disk using MS-DOS before starting the installation process.

3RD PARTY .BID FILES

If third party .BID files are being used for the disk, then copy them to the HPFS recovery disks as well as to the installation disks--they are needed during the recovery process.

LM VERSIONS EARLIER THAN 2.2

For versions of LAN Manager earlier than 2.2, the mirror of the boot partition must end up with only one partition on it. A disk with an HPFS boot partition and an additional FAT partition has been successfully mirrored and the boot partition recovered when the primary drive was removed from the system. Mirroring a boot partition onto a smaller drive is possible, but this requires that the boot partition be smaller than the mirror drive--small enough to fit onto it and leave room for fault tolerance (2 MB of unpartitioned space for smaller drives, 2% - 5% for larger). Once the boot partition has been mirrored, the remaining space on the primary drive can be partitioned. Because fault tolerance makes decisions about what raw space to use for mirroring, you must make sure that the boot mirror contains only one partition. As a result, these configurations are generally not recommended unless you have a thorough understanding of how mirroring is done.

For these versions of LAN Manager, a boot drive with two HPFS partitions will seem to mirror successfully, but attempting FTBOOT after removing the primary drive returns a message that the disk was improperly configured for recovery.

LM VERSIONS 2.2 AND LATER

For LAN Manager 2.2, mirroring of the boot drive with more than one partition is possible.

If you are using the Network Productivity Pack, copy FTBOOT.EXE from the LAN Manager 2.1 disks to the HPFS recovery disks. FTBOOT.EXE was not included on the distribution disks of the Network Productivity Pack.

If you have LAN Manager 2.2 and the date of FTBOOT.EXE is earlier than March 1993, then you need to get a newer version that fixed a bug causing Trap Ds and Cs on reboot after using FTBOOT. This fix was included in the LM22 Patch.