Which is faster, NDMPcopy or vol copy?

After posting my last post I got few mails asking, amongst ndpmpcopy and vol copy, which one would be faster?

Only if I have to count speed then vol copy, because it copies blocks directly from disk without going through FS, however I think it’s well suitable if you want to migrate a volume.

Pros

• CPU usage can be throttled
• Source volume snapshot can be copied
• Simultaneously 4 copy operations can be started
• Once started it goes to background and you can use console for other purpose 

Cons

• Destination can’t be root volume
• Destination volume should be offline
• All data in destination volume will be over-written
• Destination volume size should be bigger or equal to source
• Single file or directory cannot be specified for copy operation
• Both the volumes should be of same type; traditional or flexible
• If data is copied between two filers both filer should have other filer’s entry in /etc/hosts.equiv file and loopback address for itself in /etc/hosts file 

However for copying data between two filers for test or any other purpose ndmpcopy is more suitable because it gives you additional control and less restrictions, which is very useful.

Pros

• Little or no CPU overhead
• Incremental copy is supported
• No limitation on volume size and type
• No need to take destination volume offline
• Single file or directory can also be specified
• No file fragmentation on destination volume as all data is copied sequentially from source volume so improved data layout
• No configuration is required between two filers and username and password is used for authentication

Cons

• Snapshots can’t be copied from source
• Console is not available till the time copy operation is running so no multiple ndmpcopy operations
• If lots of small files has to be copied then copy operation will be slower 

So as you have seen both are well however one can’t be replaced for other and both have their usage for different purposes.

How to copy files in Ontap

As soon as someone asks this question we all say ‘use ndmpcoyp’ but what if you don’t have any network adapters configured, will ndmpcoyp work?

No; ndmpcopy is very useful if you want to copy a file or a whole volume however one thing very few people know that it doesn’t work if you don’t have loopback adapter configured because ndmpcopy passes all the data through lo adapter so it’s not only dependent on lo’s availability, its speed also. So how do you copy the data if lo is not available?

The answer is simple, use dd, just an old fashioned unix command which does lot of thing, not only it can copy the file with full pathname you can even use block number and disk number and the best part, syntax is simple ‘if’ for from and ‘of’ for to.

It can be used not only for copying file around the system, in fact you can use it for testing I/O and copying file from snapshot also and this command can be used regardless of permission.

A little note, if you are afraid of going in advanced or diagnostic mode better keep use rdfile and wrfile because this command is not available in admin mode so you have to go in advanced mode to use this.

Here’s the syntax of this command.

dd [ [if= file ] | [ din= disknum bin= blocknum ] ] [ [of= file ] | [ dout= disknum bout= blocknum ] ] count= number_of_blocks

Another note, if you are using count make sure you are using in multiply of 4 because a WAFL block size is 4k.

Example:

sim1> priv set advanced
sim1*> dd if=/vol/vol0/.snapshot/hourly.2/etc/snapmirror.conf of=/vol/vol0/etc/snapmirror.conf1