To build a backup environment it is recommended to follow the 3-2-1 rule.
- Make 3 backups
- Make 2 backups on different media
- Make 1 backup in another location than the source data
To carry out the third tip, we very often think of the Cloud; it’s a great solution but the costs are still quite high if we need to move TB. If, on the other hand, we have to save some GB, the solution is attractive.
For companies that need to move TB of data, a solution can be backup to a remote location, for example connected with a vpn. The costs of saving the data will therefore be absorbed by the purchase costs of a fairly large NAS unit.
Let us try to detail such a solution.
Backup speed in vpn
The speed of the backup will be determined by the slowest internet connection speed between the 2 locations. Let’s suppose that the 2 offices are able to communicate at the speed of 300 Mb / s.
300 Mb / s = 300,000,000 b / s
300,000,000 b / s / 8 = 37,500,000 b / s = 37.5 MB / s
To move 1GB of data over a 300 Mb / s network, it will take 1,000 / 37.5 = 26.7 seconds
To move 1GB of data over a 100 Mb / s network, it will take 1,000 / 12.5 = 80 seconds
Backup software all have the ability to perform incremental backups but the first backup that is performed will inevitably be very long. So it needs to be planned carefully.
If we want to move a 20GB virtual machine across a 300 Mb / s network, it will take about 27 minutes. It will take us 2 hours and 15 minutes for a 1TB virtual machine. The incremental backups of the various software on the market, in “normal” conditions of server activity, allow subsequent backups to arrive at times equal to 20% of the first backup.
Choice of Backup NAS
The source site data is stored on Nas at the destination site. It is clear that choosing a NAS equipped with a 10Gb / S ethernet card does not improve our remote backup since the transfer speed of the vpn is less than 1Gb / s.
Could the NAS disks further decrease the copy speed? To answer this, let’s take a look at a table that tries to give a value to the write speeds of the various disk systems. We took the data from the wikipedia site and then processed it.
| Drive
(Type / RPM ) |
MB/s
(64KB block, random) |
MB/s
(512KB block, random) |
MB/s random
average |
MB/s
(large block, sequential) |
MB/s sequenzial
average |
| FC / 15 K | 9.7 – 10.8 | 49.7 – 63.1 | 33,3 | 73.5 – 127.5 | 100,5 |
| SAS / 15 K | 11.2 – 12.3 | 58.9 – 68.9 | 37,8 | 91.5 – 126.3 | 108,9 |
| FC / 10 K | 8.3 – 9.2 | 40.9 – 53.1 | 27,9 | 58.1 – 107.2 | 82,65 |
| SAS / 10 K | 8.3 – 9.2 | 40.9 – 53.1 | 27,9 | 58.1 – 107.2 | 82,65 |
| SAS/SATA / 7200 | 4.4 – 4.9 | 24.3 – 32.1 | 16,4 | 43.4 – 97.8 | 70,6 |
| SATA / 5400 | 3.5 | 22.6 | 13,05 | 47,1 (estimate) | |
| SSD | 520 | 520 |
Backup software normally writes disks sequentially, so numbers in hand, even a sata 5400 hard drive could be useful in our scenario. Buying hard drives above 7200 rpm, on the other hand, would not lead to an improvement.
