I have never seen a method of shrinking a LUN that I trust personally.

It's easy to chop off the end of a LUN. ONTAP can easily truncate the LUN. The problem is the filesystem itself. Before you lop off the end of a LUN you have to make sure there is no important data on that region of the disk.

The procedure ends up being this:

1) Find a way to move filesystem data away from the region of disk you're about to chop off.

2) Find a way to update the filesystem metadata itself so it no longer knows about the region of disk you're about to chop off.

3) Shrink the disk. The word "truncate" is probably more accurate.

I once tried to follow a procedure to shrink a LUN on Solaris with ufs and managed to corrupt all my data. I did do it successfully with Windows once, but the procedure was tedious, and if you do your math wrong when performing the final LUN resizing you'll corrupt your data and you might not even notice right away.

All things considered, I'd migrate rather than try to shrink a LUN again. With a little help from rsync/robocopy you can usually make the cutover disruption minimal.

From: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] On Behalf Of Klise, Steve Sent: Monday, January 04, 2016 10:39 PM To: Kevin Richards; Toasters@teaparty.net Subject: Re: SnapDrive shrink lun

I did a quick search, and it sounds like if you can do the data migration, that would be the “safer” route to take. Might want to review this based on what flavor of ontap you are running.

https://kb.netapp.com/support/index?page=content&id=3014860&locale=e...

Thanks

Steve Klise Consulting Solutions Architect – Data Center World Wide Technology Inc. 408-242-4086 Cell

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From: <toasters-bounces@teaparty.netmailto:toasters-bounces@teaparty.net> on behalf of Kevin Richards <krichards1024@gmail.commailto:krichards1024@gmail.com> Date: Monday, January 4, 2016 at 1:31 PM To: "toasters@teaparty.netmailto:toasters@teaparty.net" <Toasters@teaparty.netmailto:Toasters@teaparty.net> Subject: SnapDrive shrink lun

Happy New Year Toasters!

Quick question for the group, we have a lun that was increased from about 3TB to 7TB. We now would like to shrink it down. My understanding is that I can only cut it by half due to a limitation of the OS (Win2008R2). My other concern is data corruption, etc. I have the option of adding a new lun and migrating data. Any recommendations from experience?

Thank you. Kevin

Just my 2 cents: I've shrinked lots of LUNs in the past and never had issues with data corruption or anything like that; client OS was a broad range from Windows 2008R2 to Windows 2012R2, IBM AIX, Debian Linux and one Solaris system. You just need to make sure to shrink the filesystem first and free up space at the end of the LUN. I do usually shrink the filesystem to a level below of what I really want to shrink it, f.ex. if I want to shrink the LUN from 7TB to 3TB, I would shrink the FS to 2.9TB and will then shrink the LUN to 3TB and increase the FS afterwards again to fill up the free space at the end of the LUN just because I'm a coward and don't trust the differnt interpretations of what a Gigabyte is worth. If you chop of one Megabyte too much, your filesystem will be in a bad state, so better to be safe than sorry.

One thing you have to take care about is LUN geometry though, a given LUN cannot be increased larger than 10 times the initial size, so f.ex. if you create a LUN with 100GB, it cannot be made larger than 1000GB which also applies to LUN shrinks (or truncates) then.

Best,

Alexander Griesser Head of Systems Operations

ANEXIA Internetdienstleistungs GmbH

E-Mail: AGriesser@anexia-it.com Web: http://www.anexia-it.com

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-----Ursprüngliche Nachricht----- Von: toasters-bounces@teaparty.net [mailto:toasters-bounces@teaparty.net] Im Auftrag von Martin Gesendet: Dienstag, 5. Januar 2016 08:48 An: toasters@teaparty.net Betreff: Re: SnapDrive shrink lun

All the methods I've seen of shrinking a LUN have the caveat of taking a backup first. I came to the conclusion that if you have to take a backup of the LUN why not just do as others have said and create a new LUN and copy the data over. It does mean you need the free space to create the additional LUN but if unless you skip taking a backup (obviously not a good idea) you're going to need space somewhere.

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