Friday, April 30, 2010

I2P (inode to pathname) in Ontap


Few days before I became curios to know what is I2P and what will happen if you turn it off. So started hunting NetApp site and Google for information however I couldn’t find much on this. Now as obvious once you are off from vendor site and Google then start looking at your social network and then, bingo! I was able to get some information on this.

So the first question what the heck is this I2P?
Actually it’s a new feature in Ontap 7.1 and later versions that maps each inode number and file name with relative path to speed up certain operations. As we all know every file, directory, soft link, hard link or any other metadata file has one inode associated with it so each inode has to go through this process and each file/directory gets 8 bits added to its metadata by Ontap whereas every hard link gets 12 bytes penalty and this happen every time you create, delete or rename file, directory or link.

Ok, but why do I need this?
As far as its usage goes there are some well known application for this like fpolicy, virus scan and file auditing which needs to know full path of the requested file whereas some are Ontap specific feature like in mixed volume it informs NFS clients for any changes made by CIFS clients; one important place where you will see difference is dump command, as having full path available for each file makes it much faster and efficient in operation, some grey areas are also there which are used by Ontap for its internal work but that’s all covered deep under their IP protection policy so I couldn’t get any info on it.

Now how to you get information about this from your system?
If you look closely you will see in vol options there is an option ‘no_i2p’ (default is off and only in 7.1 and later) to enable or disable i2p feature as well if you go to advance mode you can see few more commands related to this like ‘inodepath’ which shows the i2p information stored in a given inode whereas ‘wafl scan status’ command shows you running i2p scans which can be aborted with 'wafl scan abort scan_id' or you can also change the scan speed with ‘wafl scan speed new_speed’ command after you list the current scan speed with ‘wafl scan speed’ command.

After having these information pushed me to think that ok so most of the volumes in my systems are NFS only and they don’t need any virus scan, neither we use dump, fpolicy or any other feature so why not to turn off and get extra juice out of system but speaking with chaps it turned out that turning off wouldn’t be a good idea though they were also not sure what will break if you turn it off and as it has very little performance impact so better to leave it untouched.

And yes it’s true it does have very less performance impact as in general we don’t do so much metadata modification that it may hurt the system with i2p workload however when you upgrade your system from an earlier release to 7.1 or later family they get very busy in creating i2p information for each and every file/directory/link etc and may run in high utilization for quite some time and at that time you may wish to use these commands to quickly pull your system back in normal state and let scan run with slow speed or one volume at a time or completely stop it if you want to revert back the system to pre 7.1 release.

I think if I get some time I would like to do an extensive testing and see what comes out however if anyone else knows please share your knowledge.
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