This page was written by Christopher Spry.
I have been trying to promote among my friends the idea of always
having at least two disks in computers: a systems disk and a backup of the system disk. I
remember trying to get IBM to do this with the early PS/2 computers in 1987!. I could not
think of a better way to insure against a catastrophic failure of the system disk. I have
used the 'two disks' approach on my IRIX Indy, Windows 95 and NT workstation systems for several years
and it has paid off handsomely when I had three system disk failures (dead disks). In each
case I was up and running again in about ten minutes. All my PCs have a removable drive in
one of the slots, for this purpose and for swapping in additional hard disk space if I
need it.
There is a range of software now to copy system disks under Windows. The 'best', for me at
least, is 'ghost'. It
handles DOS, Windows 95, Windows NT, LINUX, and other partitions, even when mixed on the
same hard disk. It can prepare an 'exact' copy of a hard disk or make a 'disk image' to a
file. Under NT, it provides ways to deal with the 'SID problem' produced by making exact
copies of NT hard disks. I keep several image files, going back a month or so, of
important computers. If your BIOS allows you to alter the boot sequence, it is possible to
'test' the backup very easily. (In my view, a backup is not complete until it has been
shown to be able to 'restore'). Down time is a problem when doing the system disk
backups with 'Ghost'. I can not see a way round this
other than doing it at less busy times of day. However, the alternative of wasted hours
while a new system disk is made, after a crash, is more than compensated for by short
interruptions (say up to 45 minutes) while a full system disk is prepared with
'Ghost'.
'Replica' tape backup software from Stac Electronics Inc., does not require the computer to be off-line, but it is slower to re-enable the computer after a crash.
Recently I installed hardware RAID level 1, to mirror two Seagate 'Cheetah 18' (ST118202LW) 18.0-GB 10,000 RPM Ultra2/Wide SCSI hard disks, as an alternative to 'Ghost', but I have not tested it in real life, yet. It uses an Adaptec RAIDPORT Ultra2/Wide RAID controller card. Alternatively, I have read that if you have an NT server which is set as the primary domain controller (PDC), you can installed a second computer to be a 'backup domain controller' (BDC). You can create manually all the same shares on the BDC as on the PDC, then use a scheduled event (the AT command) to SCOPY all the data from the PDC to the BDC at regular intervals. SCOPY preserves permissions etc. If the PDC PC fails, replace it with the BDC computer. Remove the old PDC computer, promote the BDC to be the new PDC and rename the BDC to the PDC's name, so that drive mapping does not have to be redone.
I prefer to backup 'usr' files (files generated by users of the computer), once or twice a day, to hard disks in a different location
in case of fire or theft or damage. For that I use FileSync v 1.54, from Windsor Software http://www.fileware.co.uk/ This synchronizes files
and directories in NT & Windows95. CmdSync v 1.0, a 'batch mode' version which is
particularly useful for updating files across networks. It can ignore the 2 second time
signature difference on identical files copied between UNIX and Windows systems.
Under UNIX, I have found out how to copy disks in the same way, using 'dd' (disk
duplicate, for identical drives) or dump/restore (for different disks) see my guide
for how this is done under SGI IRIX. 'dd' on UNIX can be done safely
when the computer is being accessed by users.
Return to the 'home page
Return to the 'computer index page'
© cspry@sghms.ac.uk. Department of Biochemistry & Immunology, St. George's Hospital Medical School, London SW17 0RE, UK. Phone +44 20-8725 5819; fax +44 20-8725 5821. This page was updated on 10 December 2001 11:27:07.