NDMP Buffer size

[vksm]

Does any one know what is the buffer size or block size for NDMP backup using Networker with LTO-3 Drives ?
And if you can share or provide me a link for the document which says this is the value it will be of great help.

Since I am getting errors like

NDMP: 3: TAPE_WRITE, size(131072) > ndmpMaxBufSize (65536)
NDMP: 3: Error processing message 0x304: error decoding arguments.

 

[605]

If you look at the NDMP specification (ndmp.org) you will read that the NDMP client is responsible for the block size. This is the NW server. Consequently, you define the block size by selecting the device type.

This is usually not a problem. However, it can become one if you share the same media between Windows and UNIX/Linux hosts as Windows SCSI drivers normally cut the block size to 64kB (see the NW Performance Tuning Guide for details).

It seems that you have such a problem in case you have Windows backup server which is now using a tape which obviously has been written by a UNIX storage node. Is this true?


In general: Although, you can use 'normal' NW backup media for NDMP backups, it is not very good due to a lot of other issues. It looks like you have done this here. I would not recommend it.

 

[vksm]

Thanks for your response

Let me tell what we have,

1. AIX Networker Server
2. We have NDMP POOL and NDMP Tape Drives assigned to the NAS Box
3. The O/S backups are having both windows and Unix go in a different pool as o/s pool on different drives attached to different storage nodes.

 

[605]

What if you label the tape - will the error go away?

 

[vksm]

No, these errors are all there in all the datamovers on the serverlogs. For different tapes / new tapes too.

 

[605]

OK. I guess that NDMP has an internal limitation of 64kB.

Try to select the block size of 64kB for the device. Then relabel the tape.