How to tune a tape drive to address poor performance during Backup or Restore

It is currently not recommended to change the block size without extensive testing of the ability to restore all types of data.

Steps to tune a tape drive for the hardware it is attached to.
1. Create a test backup of about 2-3 gigs of data.
2. Run the job to get a baseline.
3. Go into drive properties and change one setting at a time,
  - To get to Drive properties: Click the Device tab, right click the drive head to be tuned, select properties, select the configuration tab.
  - These settings need to be set for each drive head
4.  Perform iteration testing to determine best performance values
5.  If increased performance than increase setting again
5a. If decreased performance, decrease setting to last fastest setting and move to next setting.
6. Test the ability to restore data
7. Fine tune settings against full production backups
8. Test the ability to restore data after any configuration change

Change setting in this order.

1. Buffer size
- The size of the buffer assigned in RAM
- This number must be a multiple of your block size.
- Typically increasing this from the default 64 to 256 generates the best results
- Verify the system is not already running low on memory

2. Buffer count - the number of buffers assigned in RAM
- Once again, I notice that going from 10-20 increases performance on some systems

3. High water count - Defines how many buffers get filled before sending data over the SCSI bus.  This acts like a throttle / load balance when multiple jobs are running to multiple drives over the same bus.

This testing takes about 30-60 minutes and can greatly increase performance of a tape drive.  Some other settings that should be tested are all the boxes for single block and SCSI pass through.  These boxes are mandatory in a SAN-SSO environment and should be tested in other environments to determine impact on performance.  

Other factors to consider is varying types of data.  Small files usually back up slower than large files.  Increasing a block size on a drive that is backup up numerous small files such as TIFF images, may cause decreased performance.  Once again, test the ability to restore data after any configuration changes.

The recommended numbers above: 64 to 256 buffer size and 10-20 buffer count has a net effect of increasing the memory allocated to staging data by 8 times.