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No performance difference between backup to tape and to disk
Hi,
I have done the following test using Legato Networker 7.4 - SP4.
I make a backup of 2 savesets of 2 different servers. Total : 100 GB.
The backup to tape runs at 120 Gb/hour.
I define a backup to disk adv_file device and make the same backup.
The destination device is a folder on my local E: drive on my Legato server.
The backup to disk runs at about the same speed at 125 Gb/hour.
I am surprised by this result.
What is the best way to increase the speed of backup to disk ?
Is there a golden rule ? Setting of certain parameters result in a significant gain.... ?
What is the best way to increase the speed ?
Rgds,
Johan
dpinink_silva
724 Posts
0
May 7th, 2010 05:00
First of all we have to check where is the bottleneck. When your file device and your tape device write at the same rate, usually that means that your network is not sending data enough to make a difference. Of course your file device can be writing slower due other problems/configurations, but I would let that as a final option.
First of all, try to copy/ftp the same amount of data from the same client over the network and check the transfer rate. If it's about 120 Gb/hour, it's time to check how to improve your network.
Second, try to write 100 Gb from your Nw server to the tape itself, that should give you the best performance rate the tape can reach. The same test but writing to the file device only works if you have different disk and disk controllers for both source and target drives.
ble1
2 Intern
2 Intern
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14.3K Posts
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June 3rd, 2010 00:00
Could it be that you use 1Gbps NIC?
mrpappa24
4 Posts
0
June 3rd, 2010 01:00
To check performance possibilities of backup devices, EMC Networker has a rather undocumented feature named bigasm.
create a .nsr or nsr.dir file (depending on OS) in any directory containing the following:
bigasm -S 10G: bigfile
then create a file named bigfile (can be zero bytes large) in that directory and use the:
save -b bigfile
command to save the file to the appropriate pool. Networker will now save 10GB of zero's to this pool, giving you optimum compression on your tape drive.
Do the same for the disk pool and see what the difference in backup speed is.
If you see comparable speeds of 100-125GB/hour, then this may be the limit of your server.
Performance tuning in general is a very hairy subject. Multiplexing to tapes may increase your backup throughput, but is likely to reduce recovery throughput, so you would need to find a balance there.
Making sure your network is capable of passing more data will require quite a bit of network knowledge as well as knowing what is happening in your network at the time of backup.
Writing to disk can be quicker than writing to tape, depending on the disk system (configuration) and the tape drive. The nicest thing about backup to disk is that you dont have to worry about getting it into streaming mode. However sending too many savesets to the same disk backup device may cause disk contention on the underlying raid system.