Backup time

[Evan]

Hi all,

Is getting in the area of 19457kb/sec write time compressed to tape good? We have LTO3 tape drives and My backups are taking a very long time. I'm assuming that either the write times are my bottleneck or it is the drives themselves. Or are there other factors that I should take into consideration? Let me know if I should be providing more information.

Thanks

Evan

[Marco_Usiminas]

Hi.

bottleneck is a point of the tape, but the compression can increase the time to back up in up to 30%. strip compression and see if the time is appropriate.

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[Kiran_Bandi]

Many other factors may also effect backup speeds other than tape drive. Some of them are

Connectivity between media server and tape drive, media Server resources like CPU,Memory,Disk I/O and available bandwidth in the network connecting the client to the media server. During incremental/differential backups, available client resources also will be a consideration. Also the type of backup. File servers backups will be comparatively slow.

If you are feeling much slower backups with respect to a client, check the connectivity between client and media server.

Regards...

[Ed_Wilts]

You should be able to get >60MB/sec on an LTO-3 with the right combination of hardware and data types.

In my experience, the tape drive is rarely the bottleneck - it's always back at the client or network.

That's to to say that I always get >60MB/sec either - I'd be ecstatic if I did.  But it IS doable.

It always astonishes me how often people upgrade tape drives because their backups are slow when the problem is typically somewhere else and putting in a faster tape drive may actually REDUCE the performance.

[mph999]

At 20MB/s the LTO3 drive is 'shoeshining' (stopping and restarting) - this quickly damages the tape and drive due to increased wear.  The LTO drives (all of them) are not designed to stop/start, they are meant to be streaming.

As a simple test on the client:

time bpbkar -nocont /path/to/backup

This will give the time taken to read the data off the disk (it makes the client do a backup, but the data is 'thrown away'.

Work out the amount of data in the filesystem, then work out the speed.

Next, using the same data, FTP 50-60 MB to the media server, just an indication, but how fast is this.

After this, you could use the bpbkar and bptm log to work out how many times NBU is waiting for a full buffer or enpty buffer.

If waiting for a full buffer many times, then this suggests the data is slow coming from he client.  If waiting for empty, it suggests it is slow going to tape.

You could also tar some data to tape (from the media server), using the os tar command (be careful to use a blank tape), load using robtest and see how fast this goes.

Could be worth checking the number and size of the DATA buffers, suggest 262144 as a value for the size, at least as a starting point.  There are technotes available that explain this.

The type of data could be a factor, if for example the client is a windows servers with 1000's of small files, it'll probably never go quickly (that'swhat Flash backup is for ..).

Martin

[Nicolai]

Follow up to mph999 fine post:

How to configure NUMBER_DATA_BUFFERS / SIZE_DATA_BUFFERS - Take a look in the "Netbackup Planing and Performance tuning guide" page 124 - Netbackup server Performance.

http://www.symantec.com/docs/TECH62317

(if the link dump to the product main page - go back and click the link again - Symantec link re-direction is broke).

update:

Just to show how much difference buffer tuning does on LTO3:

Before tuning: 19MB/sec (default values)

Second tuning attempt: 49MB/sec (using 128K block size, 64 buffers)

Final result: 129MB/sec  (using 128K block size and 256 buffers)

I suggest you start resolving the issue by doing buffer tuning as you are getting the "before tuning" speed.

[mph999]

Thanks Nicolai ...

... and just to add to Nicolais post ...

1.  Tuning via number and size of data buffers is trial and error, you just have to try it and see what happens.

2.  Increasing the number of buffers does not always help, if we aren't filling them quickly, having a larger number makes no difference.

3.  A larger number of buffers (or size) requires more memory ...  These data buffers are held in physical memory, the data is sent there before going to tape, like filling a bucket with water.  The more or bigger the buckets, the more mmory.

Thanks,

Martin

[Amit_Karia]

do u have a dedicated network infractructure of backups? if not so and u are experincing issues with all backups, its always a good practise to have dedicated network for backups

If volume of data being backed up is large , Assuming your client is conncted to SAN.You can configure your client as a media server by zoning your client with tape drives connected to san switch (You must have sso) license for the same. And then installing netbackup media server software on your media server

[Amit_Karia]

Also provide more info. like OS of your master server,no. of media servers,no. backups running simultaneously, Multiplexing and multistreaming configuration etc.