Now we have multiple media servers – so the 3 key components could run on
one or more boxes so here the Master Backup Server would tell our backup
client that it’s your turn to backup. It would advise you are using this resource
(this particular media server). So now the backup client reads the files that it
has got to back up, copies them over the Local Area Network, they go through
the media server. The media server understands the file structure. It builds
the tape index. When the data gets written to tape a catalogue is constructed
as it goes through. Once it’s done the catalogue gets passed back to our
backup server and is stored there. So the backup server has a list of what is
on what tape, the files and the positions etc. So if we needed to do a restore it
knows what tapes and where on those tapes it needs to restore the
By having multiple media servers we can start interleaving and multiplexing
our data streams to different devices and different servers. But the LAN is
probably going to be our bottleneck. So at this point all of our data is
traversing our Local Area Network. But if our LAN sits idle overnight this is
probably going to be the lowest cost and most easily understood solution.
LTO-2 tape drives run at 35MB/s raw.
Most of us probably use 2:1 compression on a tape drive and that means
70MB/s a second and our LAN is probably Gigabit Ethernet. So that means
one LTO-2 pretty much saturates a Gigabit Ethernet network.
If you go to something like an LTO-3 this will run at 68 – 80MB/s raw.
So that’s 136 – 160MB/s at 2:1 compression which means the LAN is now the
If the LAN is the bottleneck our tape is going to shoeshine due to buffer
What will happen is that when we write data, we fill up the buffers at 100MB/s,
the tape empties them at 136MB/s.
So really, 1Gb/s Ethernet = 1 LTO-2 drive.
If you want to start using faster drives like LTO-3 or LTO-4 you have to put it
onto 2Gb/s and 4Gb/s Fibre Channel infrastructure.