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Re: Incorrect Free Space / xfs_growfs on RAID5 Volume ?

To: xfs@xxxxxxxxxxx
Subject: Re: Incorrect Free Space / xfs_growfs on RAID5 Volume ?
From: Svavar Örn Eysteinsson <svavar@xxxxxxxx>
Date: Wed, 27 May 2009 09:26:10 +0000
In-reply-to: <4A1BE48F.9020107@xxxxxxxxxxxx>
References: <BC442FE9-64FC-4F3C-A5AA-25C890AABD3C@xxxxxxxx> <4A1BE48F.9020107@xxxxxxxxxxxx>

I read on 
that if your kernel is compiled with CONFIG_LBD You can break the 2tb limit. Any facts on that ?

Breaking 2TB Option 2 - Use Linux with CONFIG_LBD enabled. Most Linux file systems are capable of partitions larger than 2 TB, as long as the Linux kernel itself is. (See this comparison of Linux file systems.) Most Linux distributions now have kernels compiled with CONFIG_LBD enabled (Ubuntu 6.10 does, for example.) As long as the kernel is configured/compiled properly, it is straight-forward to create a single 4TB EXT3 (or similar) partition.

* To summarize: 1 RAID array of five 1TB Drives -> 1 RAID level 5 Volume Set that is 4TB -> 1 EXT3 (or similar) Linux partition that is 4TB.

.... Is this maby out of my scope/setup ?

Is there a simple way for me to check if my kernel has this option compiled in ? I'm running Fedora Core 6 with #1 SMP Tue Nov 25 11:50:10 GMT 2008 i686 i686 i386 GNU/Linux.

And the FINAL question.... Is there any way for me to alter the raid volume, partitions to GPT or just format the /dev/sdb without loosing any data ?
Maby it's just not possible without backup up data, and restore'ing ?

Thanks allot guys..

Best regards,

Svavar - Reykjavik - Iceland

On 26.5.2009, at 12:46, Michael Weissenbacher wrote:

Hi Svavar!
Now the strange part. When I issue “df -h” command it shows much smaller
disk space added then it should have.

You have run into the 2TB limit for a DOS Paritition Table. You must use GPT (GUID Partition Table) to overcome the limit. You can't use fdisk for that since it has no GPT support. An alternative would be parted [1]. I'm not sure how this can be done without data loss. An alternative would be to not use partitions at all and create the XFS directly on /dev/sdb.
This is not really an XFS issue but an partitioning issue.

[1] http://www.gnu.org/software/parted/index.shtml


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