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How to find maximum block size for tape device.

Stiva
Level 4

Hi All,

 

We have netbackup 7.1 installed on Solaris server. We are using LTO4 & LTO5 tapes for backup. I need a help to find the maximum block size for LTO4 & LTO5 tapes. Is there any way to find it out from netbackup end.

Some NDMP jobs are there in my environment and Data buffer size for NDMP is 64kb which reduce the backup throughput. I wanted to change it to 256kb for better performance but before that I wanted to check the maximum block size of tape.

Thanks in advance.

 

 

2 ACCEPTED SOLUTIONS

Accepted Solutions

mph999
Level 6
Employee Accredited

Max size is dependant on the tape drive itself, or HBA etc ... no way to tell from NBU without testing to see what works (backup and restore).

However, the vast majority of people use 256k (262144 in SIZE_DATA_BUFFERS) along with 126 or 256 for the number of buffers.

Have a look at this:

http://www.mass.dk/category/netbackup-guides/

Credit to Nicolai - it's his site but he gives a good explanation so I'm sure he won;t mind me posting it.

Martin

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Nicolai
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Direct NDMP where the device is writing its own data to tape, Netbackup is merely a control station and out of the data loop. Depending on the vendor (Neapp, EMC) and firmware revision, they may have a issue with other settings than the default. Best way to verify is look in the vendors documentation.

If firmware revision of the NDMP device is relative new (+/ 2 year) I would not be worried.

@Stiva: What kind of NDMP operation do you plan to use ?

Some of the NDMP method is described in Netbackup NDMP admin guide 

http://www.symantec.com/docs/DOC6456

Despite the warnings, I still think its a good idea to change block size to 256K.

 Just taking little precaution before implementing any idea.

This is also called "taking yore job serious" - credits for this from me :)

View solution in original post

14 REPLIES 14

sdo
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Whilst in some scenarios tape block size can be a NetBackup configurable element, really the maximum block size is an attribute of the tape drive itself and not NetBackup.  However, HBAs can have a maximum too.  And the HBA driver and/or tape drive driver can have maximums too.

So, the true achievable maximum is the lowest of the highest values supported by tape drive and/or HBA and/or HBA driver and/or tape drive driver and/or NetBackup.

Be careful though - you refer to NDMP - please describe your NetBackup for NDMP config?  Direct?  Three-way?  Remote?

sdo
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So, how to find the maximum?

Research at least the five above elements... tape drive, HBA, HBA driver, tape drive driver, NetBackup.

Choose a test value.

Test backup, and you must test restore when changing tape drive block size.

Beware the implications!  Do you want/need to restore at another site?  e.g. production site infrastructure may support a 256KB or 512KB tape block size - but the DR site might not!... and so, no restores at DR site!!

mph999
Level 6
Employee Accredited

Max size is dependant on the tape drive itself, or HBA etc ... no way to tell from NBU without testing to see what works (backup and restore).

However, the vast majority of people use 256k (262144 in SIZE_DATA_BUFFERS) along with 126 or 256 for the number of buffers.

Have a look at this:

http://www.mass.dk/category/netbackup-guides/

Credit to Nicolai - it's his site but he gives a good explanation so I'm sure he won;t mind me posting it.

Martin

Marianne
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Use robtest to mount a tape in a drive, then use nt_ttu  command to list parameters.

See this TN (ignore the topic): http://www.symantec.com/docs/TECH22746 

1. From the <install path>\Veritas\Volmgr\bin directory type the following command: 
nt_ttu 
nt_ttu> 
2. At the nt_ttu> prompt, type "p" and press enter (without the quotes): 
nt_ttu> p 
This will list specific tape drive parameters.  
3. Record the value for "maximum blocksize" 

Nicolai
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I would take a look at this tech note - but do test it very carefully. Not alle NDMP devices can do 256K block size.

DOCUMENTATION: What is the SIZE_DATA_BUFFERS_NDMP tuning file?

http://www.symantec.com/docs/TECH51967

Thanks MPH999 for the reference :)

Stiva
Level 4

Thank you all for your replies.

@Marianne : Given technote is for windows server. Will it work on Unix servers also?

@Nicolai : I am confused here "Not alle NDMP devices can do 256K block size.". How do I get to know that which NDMP devices can do 256K block size. 

I will try all suggetions provided here.

I have just joined new organization, Just taking little precaution before implementing any idea... :) 

 

 

 

sdo
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Yes, 'robtest' should be applicable to any media server.

.

Take a look at the NetBackup Blueprint for NDMP, linked here:

https://www-secure.symantec.com/connect/forums/list-netbackup-blueprints

...to first understand your NDMP config.

Once you know which model of tape connectivity you have, this will reveal your options to you.

Stiva
Level 4

Hi Sdo,

Not about robtest. I am asking about command nt_ttu.

I will check it tommarow and update you all.

Thanks for NDMP blueprint. I will refer it.

 

 

 

Marianne
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robtest can only be used on the robot control host to mount a tape. Sorry, I don't know if the command exist on *nix servers. I don't have access to a server to check, but I have never heard of a *nix or NDMP server with a problem with 256K block size.

Nicolai
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Direct NDMP where the device is writing its own data to tape, Netbackup is merely a control station and out of the data loop. Depending on the vendor (Neapp, EMC) and firmware revision, they may have a issue with other settings than the default. Best way to verify is look in the vendors documentation.

If firmware revision of the NDMP device is relative new (+/ 2 year) I would not be worried.

@Stiva: What kind of NDMP operation do you plan to use ?

Some of the NDMP method is described in Netbackup NDMP admin guide 

http://www.symantec.com/docs/DOC6456

Despite the warnings, I still think its a good idea to change block size to 256K.

 Just taking little precaution before implementing any idea.

This is also called "taking yore job serious" - credits for this from me :)

mph999
Level 6
Employee Accredited

You are welcome, don't delete that page, I use it quite a lot ....

;0)

I even use it with customers sometimes ...

"If you don't believe me, go and look at this page ..."

 

mph999
Level 6
Employee Accredited

"@Marianne : Given technote is for windows server. Will it work on Unix servers also?"

No ...

nt_ttu is a windows only command,

I'd have to look to see if any available unix commands can show the same details, maybe scsi_command can do it, I've never looked for that particular information from drive so I don't know for sure.

The chap who originally wrote nt_ttu is one of my colleagues in the UK, if he added that exact feature I don't know (Engineering took over looking after the command and may have added to it since it was originally available) - anyhow, he may know a way of doing it so I'll ask him.

TBH though, all modern drives can cope with 256 (so LTO and equiv) - and 512 has worked when I've tried it, there is no reason to think of going higher as 256 often gives the best performance.

To find the max BS for an ndmp device, you'll have to either test it or ask the vendor.

 

Regards,

 

martin

Stiva
Level 4

Thanks Nicolaie..

 

We are using Direct attached NDMP. Will refer NDMP guide for sure.

 

For now raised case with vendor. They said ok to increase block size 256Kb it will support by tapes but they are also not sure about Maximum block size of tape.

Now there is not any option without testing it on backup.

Thank you all for your valuable inputs. I will be back with results after implementation.

Nicolai
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Stick with a 256K block size - you don't gain much (if any) using a 512K block size.