Tape Backup performance issue with a PE2950 with MD1000

[John LLOYD]

> Date: Fri, 03 Oct 2008 16:50:13 +0200
> From: " R?nnblom Jan?ke  /Teknous"
> 	<jan-ake.ronnblom at skeria.skelleftea.se>
> Subject: Re: Tape Backup performance issue with a PE2950 with MD1000
> 	RAID 5arrays 	attached
> To: "linux-poweredge" <linux-poweredge at dell.com>
> Message-ID:
> 	
> <fc.00864af50c7ffc213b9aca00e78e9b55.c7ffccd at student.skelleftea.se>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> Hi,
> 
> First I don't think you would gain anything by replacing the LTO3
> drives since your not pushing them to their limit today.

I agree with this comment -- your LTO3 should be running a bit faster
than 30MB/s especially if the data is compressible.  60 is not
unreasonable if the files are large and compressible.

> 
> Second. What kind of files are stored on the disks? Are they small
> or large? Millions of them or only a few thousand? Do you use the
> SATA disks for backup to disk?

There was a previous posting from somebody with lots of 25kbyte files --
the seek times dominated the disk performance so his LTO3 would never be
fed fast enough.  I think he moved to a disk-based backup using tar and
copied those backups to tape.

> 
> Have you read the NetBackup Performance Guide? Which version
> of NetBackup are you running?
> 
> http://seer.entsupport.symantec.com/docs/307083.htm
> 
> You might need to tune BUFFER_SIZE among a few things
> and then probably the Linux kernel also. You could also measure
> the speed to the LTO3 drives with dd and different buffer sizes
> to determine the sweet-spot!

I agree with the comment that Netbackup can be tuned, and must disagree
with how -- don't change the buffer size, which will make your Netbackup
tapes incompatible with any other installation, just change the buffer
COUNT.

echo 32 > /usr/openv/netbackup/db/config/NUMBER_DATA_BUFFERS

The default is something tiny like 2 or 3.

Also, run the newest possible version of Netbackup -- older versions
have scheduling and security defects.


--John