Backup and Restore to Multiple Tapes

Our next set of experiments are designed to measure how effectively each dump strategy can use parallel backup tape devices. For the logical strategy, we cannot use multiple tape devices in parallel for a single dump due to the strictly linear format that dump uses. Therefore we have separated the home volume into 4 equal sized independent pieces (we used quota trees, a Network Appliance construct for managing space utilization) and dumped them in parallel. For physical dump, we dumped the home volume to multiple tape devices in parallel. Tables 4 and 5 report our results.

   

Table 4: Parallel Backup and Restore Performance on 2 tape drives

Operation	Elapsed time	CPU Utilization	Disk MB/s	Tape MB/s
Logical Backup
Mapping	15 minutes	50%	5.0	0.0
Directories	15 minutes	40%	15.0	12.0
Files	4 hours	50%	12 - 20	12 - 20
Logical Restore
Creating files	1.25 hours	53%	6.0	0.0
Filling in data	3.5 hours	75%	16.0	16.0
Physical Backup
Dumping blocks	3.25 hours	12%	17	17
Physical Restore
Restoring blocks	3.1 hours	21%	17.4	17.4

   

Table 5: Parallel Backup and Restore Performance on 4 tape drives

Operation	Elapsed time	CPU Utilization	Disk MB/s	Tape MB/s
Logical Backup
Mapping	5 minutes	90%	9.5	0.0
Directories	7 minutes	90%	27.0	12.0
Files	2.5 hours	90%	21	21
Logical Restore
Creating files	0.75 hours	53%	9.0	0.0
Filling in data	3.25 hours	100%	18.0	18.0
Physical Backup
Dumping blocks	1.7 hours	30%	31	31
Physical Restore
Restoring blocks	1.63 hours	41%	32	32

Overall, logical dump managed to dump the 188 GByte home volume to 4 tape drives in 2.7 hours, achieving 69.6 GBytes/hour, or 17.4 GBytes/hour/tape. Physical backup to 4 drives completed in 1.7 hours, achieving 110 GBytes/hour, or 27.6 GBytes/hour/tape.