Backup throughput metrics

When planning your backup strategy you need to consider the path that data takes to your backup servers and from there to your tape drives or disks. Whichever is the slowest point in the chain will determine just how fast your backups can run.

Below are some metrics that give rough throughputs for networks, backup devices etc to help you plan your backup and know in advance just what sort of throughput you are likely to get. All you then need to do is multiply the slowest link in your chain by the number of hours of your backup window and then you know just how much data you will be able to backup – remember that bonding cards together or adding backup devices to a tape library will increase your data throughput (simply multiply the figures below).

Network Transfer Rates

Network Type Theoretical Rate Realistic Throughput Realistic Rate
10 Base-T 10 Mbps
1.25 MB/sec
40 – 50 percent 500 KB/sec
1.8 GB/hr
100 Base-T 100 Mbps
12.55 MB/sec
80 percent 10 MB/sec
36 GB/hr
1 Gigabit 1000 Mbps
125 MB/sec
70 percent 87.5 MB/sec
315 GB/hr

SCSI Transfer Rates

Version Bus Width Approximate Maximum Data-Transfer Rate
Wide Ultra SCSI 16 bits 40 MB/sec
144 GB/hour
Ultra2 SCSI 8 buts 40 MB/sec
144 GB/hour
Wide Ultra2 SCSI 16 bits 80 MB/sec
288 GB/hour
Ultra160 SCSI 16 bits 160 MB/sec
576 GB/hour
Ultra320 SCSI 16 bits 320 MB/sec
1,152 GB/hour

Fibre Channel Transfer Rates

Version Bus Width Approximate Maximum Data-Transfer Rate
Fibre Channel 1 Gbps 100 MB/sec
360 GB/hour
Fibre Channel 2 Gbps 200 MB/sec
720 GB/hour
Fibre Channel 4 Gbps 400 MB/sec
1,440 GB/hour
Fibre Channel 8 Gbps 800 MB/sec
2,880 GB/hour

Tape Drives

Device Type Approximate Transfer Rate Maximum Capacity
DDS-4 6.0 MB/sec or 21.6 GB/hour 40GB
AIT-2 12.0 MB/sec or 43.2 GB/hour 100 GB
AIT-3 31.2 MB/sec or 112.3 GB/hour 260 GB
DLT 7000 10.0 MB/sec or 36.0 GB/hour 70 GB
DLT 8000 12.0 MB/sec or 43.2 GB/hour 80 GB
Super DLT 24.0 MB/sec or 86.4 GB/hour 220 GB
Mammoth-2 24.0 MB/sec or 86.4 GB/hour 160 GB
Ultrium (LTO) 30.0 MB/sec or 108.0 GB/hour 200 GB
IBM 9890 20.0 MB/sec or 72.0 GB/hour 40 GB
IBM 3590E 15.0 MB/sec or 54.0 GB/hour 60 GB
LTO2 68.0 MB/sec or 245.0 GB/hour 400 GB
LTO3 160.0 MB/sec or 576.0 GB/hour 800 GB
LT04 240.0 MB/sec or 864.0 GB/hour 1.6 TB
DLTS4 320.0 MB/sec or 1,152 GB/hour 1.6 TB

So, don’t buy a DLTS4 drive to run over a 1GB link, you may as well save some money and buy a less capable drive as your link will slow you down. And do consider streaming multiple backups to the same backup device or using multiple older backup devices to take account of faster links.