Throughput problems

[Raid5]

I used to have 2 DLT 8000's. I have replaced those with 2 new HP LTO 1/9's. The backup software that I am using is Arcserve IT 6.61. My quesion is "Why havent' my backups gotten any faster"? DLT Throughput is light years behind LTO and yet my backups are still crawling. Could it be that arcserve cannot give data to the drive fast enough. Or is HP pulling our leg about drive performance.

 

[mewa]

The drive performance is not the only factor which can improve/damage the backup speed.
The drive should work in streaming mode. That means you have to be able to read and transfer the data fast enough. Not working in streaming mode the performance is very poor.
There are many points where you can lose the possibility to work in streaming mode:
- hard disks are slow
- LAN is slow
- backup/production server is slow
- backup software is slow
- software compression in switched on

To feed 2 LTO drives to make them work concurrently in streaming mode you have to get a data througput of at least 12 MB/s (LTO streaming mode is between 6 and 15MB/s).
But LTO drives are able to write up to 15MB/s which means 30MB/s for 2 drives. So if you backup via 100Mb LAN you are a looser, because this LAN can give you only 7MB/s, which is enough for DLT, but too small for LTO.
If you backup locally (local hard drives and locally connected LTO) check how fast you can read from your hard drives.
Let me know some more details of your backup environment to help you find out why the speed is not good.

mewa

 

[Raid5]

We have a 100 MB switched network. All servers are plugged directly into a cisco 5500 series route switch. Compaq 1850R with NT 4.0. Ultra SCSI 2 HD's. Hardware mirrored OS "I know it could be faster". Arcserve reports that it will backup locally @ around 850 MB per Minute. Across the network it will top out at around 430 MB per Minute. I think that the local backup is only about half of what the drive is capable of. Backup server has a Smart -3200 Controller in it.

How did you get 7 MB a second on a 100 MB switched network.

Any more information that you need I will happily give you.

 

[mewa]

I meant 100BT LAN which is 12MB/s lan and normaly you get about 60% of it, which is 7,5MB/s.
HDs should not limit the backup speed. This is also reported by arcserv, which claims can backup locally with speed of 850MB/min which is 14MB/s. And I guess it is right.

In my opinion your problem is your network - those 7MB/s (maybe 10 if you are lucky).
What I would test is:
1. Backup to one LTO drive only and check the speed.
2. Backup a disk which is local to media agent, so to exclude the network as the one which causes the problem and check the speed
Also how much data do you back up? If there is only little data during test backup you results may not make too much sense.

BTW, what was the speed of your backup to 2 DLTs concurrently? Was it via lan? How many servers were backed up concurrently?

Bye,
mewa

 

[itmontyp]

We hasd a similar problem but with just one autoloader.

I found the problem to be Antivirus software running on the networked servers being backed up

Turn it off and got approx 500% throughput

Cheers

ITMontyp