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New Member

slow backup over WAN

I have a problem when backing up over the WAN. I have a 768k in/out Frame relay circuit between sites. When backing up a server (at midnight)it takes 6-10 hours to back up 1.6gig. Does this make sense? Can I optomize the router to improve the time it takes? I have a 3640 on one end and a 2507 on the other....

New Member

Re: slow backup over WAN


You did not indicate what the CIR value was on the ckt.

You can optimize the router by giving packets between these two hosts highest priority using customer or priority queuing as a test to see what happens. You can also use a time based access-list to simply block all traffic except that between your two end stations for x amount of time to see what happens. This would be a good test to see if it is something other than a bandwidth issue.



Re: slow backup over WAN

Well, Lets do the math:

Your WAN link = 768,000 bits per second.

768,000 bits per second divided by 8 = 96,000 Bytes per second.

So, if you have to transfer 1.6 GigaBytes ....

1,600,000 Bytes / 96,000 Bytes/sec = 16667 seconds

16667 seconds / 60 = 278 minutes

278 minutes / 60 = 4.62 Hours

So, it would take 4.62 Hours to transfer 1.6 GigBytes over a 768K WAN link assuming that you would get 100% efficiency from the WAN link 100% of the time not counting any overhead. This would never happen. Realisticly, your best case scenario would be around 80% efficiency. Which would look something like this...

96,000 Bytes/sec * .80 efficiency = 76800 Bytes/sec

1,600,000,000 Bytes / 76800 Bytes/sec = 20,834 seconds

20,834 seconds / 60 = 347 minutes

347 minutes / 60 = 5.8 Hours

5.8 Hours is pretty close to your observation of 6-10 hours. You might only be getting 50-60% efficiency from WAN link due to overhead and the bursty nature of your data transfer. All in all, the performance you have observed is not way off from what you should expect.


Brad H.