Unfortunately this is all just theory. The reality is a bit different. You forgot that every packet on the network has to be processes and transported over multiple busses before it reaches the tape drive. These times add up to quite a bit. I have Gigabit ethernet, I have powerfull backup machines that perform at 20 Mbyte/sec on backup of ordinary Windows NT servers over LAN. These machines backup about 1.5 TB spread over 100+ servers in about 20 hours. But afte many tests the same machine with Gigabit Ethernet has only been able to backup a single filer with 4 volumes @ 139GB at a rate of about 48 GB/Hour.The Gigabit idles at that throughput. The equation that Gigabit is 10x Fast Ethernet does not work on a point-to-point situation.

Bye Ernie

-----Original Message----- From: Jay Orr [SMTP:orrjl@stl.nexen.com] Sent: Thursday, April 13, 2000 11:22 PM To: toasters@mathworks.com Subject: RE: Need new backup solution

On Thu, 13 Apr 2000, Schepers, Jan wrote:

...

Looking at the responses sofar, most of you agree on: o directly attached tape devices and o the use of NDMP software

If I may put my 2 cents worth in...

First of all as I understand NDMP (which isn't that well - feel free to enlighten me if I'm mistaken) it's just a different standard of dump of sorts, so other then being able to dump a netapp directly connected tape drive there is no advantage to using it (i.e. if you're backing up over a network, same performance of dump vs. NDMP backups). This would put the two points above together as one.

Second, direct connect isn't necessarly the fastest - for instance, many tape drives have throughput of less then 10M Bytes/sec. If you have 100Mb ethernet, thats ~11M Bytes/sec, so you're getting the same throughput and the bottleneck is still the tape drive. If you have a seperate "backup" network of 100Mb ethernet and backup through the network, time is saved if you use a backup package that interleaves backups (i.e. combines backup streams) - then the tape drive isn't waiting for one machie to feed it data. Kick this up to Gigabit and you would outperform the tape drive. Also, with this method you have less unused backup media and better media inventory management.

However, there are things that can affect throughput of networked backups

• NFS latencies, traffic on the ethernet, etc.

SO, as I see it, there isn't really a quick-and-dirty rule of thumb on this. The factors that would have to be considered are :

1. Tape throughput
2. Network throughput
3. Backup software methodology.

all of these weigh close to equal in the equasion of "what's the best way to do it", so unfortunately I don't see an easy rule of thumb..

Of course, I'm never one to trust an easy answer either - so maybe it's just me ;p

---

Jay Orr Systems Administrator Fujitsu Nexion Inc. St. Louis, MO