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Converting GFS in to ext3 - Redhat cluster (RHEL 5)

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unix adm
Regular Advisor

Converting GFS in to ext3 - Redhat cluster (RHEL 5)


I have Redhat cluster (active passive)installed on two of RHEL 5 server ( 2 * bl860c) , right now we are running with GFS file system however during the test GFS has been found performing badly and application team wants to go to Ext 3 . Ext 3 has been tested and seems performing 2 times better with respect to I/O by apps team.

Question 1 - In order to change GFS file system to Ext 3, what are the steps installed , do I need to only recreate the file system or recreate the whole cluster?

Question 2: Any simplified document for creation of Redhat cluster? I have one from Redhat , I want something very precise?

Steven E. Protter
Exalted Contributor

Re: Converting GFS in to ext3 - Redhat cluster (RHEL 5)


1-Back up the data, use newfs to lay down a new file system, restore data. Do not trust short cuts in this area.

2-If you might share the document link you have, I could avoid giving you the same document you are already using. Bottom line is clustering is not simple, and you probably have a good document already.

Steven E Protter
Owner of ISN Corporation
unix adm
Regular Advisor

Re: Converting GFS in to ext3 - Redhat cluster (RHEL 5)

HI Steven ,

Thx for ur response, I did the similar steps.

1) Shtdown the service.
2) Removed the GFS resource from service. (service > Edit service properties)
3) Removed the resource.
4) Recreated the VG with ext3.

4) Recreated the VG with ext3.


vgexport XXXXXXXXX

pvcreate â ff XXXXXXXXXX

vgcreate â s 32 XXXXXX XXXXXXXXXX

lvcreate â L 1012G XXXXXXXXX


5)Re added the resource with file system option

6) Added the resource to service

7) Restarted the cluster moved the services here and there seems to be happening OK.

The document I followed downloaded from this link and seems OK for now.

Questions 1 - Did I miss anything on the above steps for reformatting with EXT3? These servers going live in few days and I am fairly new to Redhat cluster and I have to be very sure.

Question 2 do I need clvmd Still running ?

Thanks in Advance
Honored Contributor

Re: Converting GFS in to ext3 - Redhat cluster (RHEL 5)

1.) Your procedure looks OK. In your step 4 the deletion and re-creation of the VG was slightly overkill: just mkfs alone in step 4 would have been sufficient. But your procedure was not harmful: you just did some extra work.

(Also note that "vgexport" does not mean the same thing in Linux as in HP-UX. It does not remove the system's knowledge about the VG: it just sets the VG state so that it will not conflict if the VG's disks are moved to another system that already has a VG with the same name.)

2.) Yes, you need to have clvmd running.

After you switched the file system from GFS to ext3, the VG must no longer be allowed to be active on two or more nodes simultaneously, because ext3 cannot handle multiple access like that. (The combination of disk caching and ext3's ignorance of other nodes' actions would quickly cause data corruption in this situation.)

The clvmd will guard that this will never happen, and will stop any attempts to activate the VG if it's already active on another node.

One of the reasons why GFS is so much slower than plain ext3 is that it needs to obtain a cluster-wide lock for many disk operations, to allow multiple nodes access the same filesystem simultaneously without stepping on each other.

I hear that this critical coordination scheme has been optimized in a few important ways in GFS2, so it might be faster once it's production-ready. I guess we'll see in RHEL 6...

unix adm
Regular Advisor

Re: Converting GFS in to ext3 - Redhat cluster (RHEL 5)

Thanks Matti,

You made it clear for me.