I'm planning to make some major backups of my WinXP Home system. I started
by trying to get an idea of the space required. Here's what I learned,
using the Windows Explorer and the Properties command on the various folders
(all in GB, and displaying hidden and system files):
C: (entire drive) 87
Program files 6
Windows 6
Data files 9
Docs & Settings 2
All other C: folders 5
Subtotal of above 28
So the apparent space occupied by all Windows Explorer displayed folders are
approximately 60GB below the total reported for the C: drive.
For backup space planning purposes, which is correct?
And why the huge discrepancy?
Besides the hidden and system files that you may not be seeing, each file
may require more space than its size. The hard drive is organized into
small "pockets" (clusters) that are all the same size. Files are divided up
into however many clusters are needed to accommodate them. There may be
leftover space (slack space) when all is said and done.
Individual cluster size depends on a variety of factors: type of file
system (NTFS, FAT32, etc), size of partition are two determining criteria.
Hard drive real estate lost to slack space is not a huge concern these days
but it is one of the reasons why adding the numbers you see in Properties
for a handful of objects doesn't always jive with what other tools report.
For backup purposes: Total disk size, minus free space = the "size" of the
files and folders to be backed up. You can reduce that final number by
doing some housekeeping before creating the backup: clearing the content of
Temporary Internet Files folder, clearing the various Temp folders,
deleting all but the recent System Restore point for starters.
Backup programs: Some will "compress" the backup file. Some allow you to
choose the amount of compression that will be used. Check the help file of
your backup program to see if it compresses backup or not. Also read
carefully sections about recommended levels of compression (overly
compressing is usually not a good thing to do).
Also in your plan, decide if you want to keep one, two or more sets of
backup. I urge to keep multiples and of multiple types- if one set is "bad"
you have others to fall back on. Also, if trying to troubleshoot a problem,
the most recent backup may suffer the same troubles and an older backup is
needed to get back to when things were "okay."
Another reason for multiples: If your backup media/hardware is damaged or
lost (an external hard drive dies, for example), you still have a backup
set on DVD or another external somewhere else.
