Re: lvm2 size of logical volume after lvcreate --size 348g after mkfs.ext3 -m 0 is only 343 gigabytes?
On Thu, Feb 14, 2013 at 3:36 PM, Mitchell Laks <mlaks@post.harvard.edu> wrote:
> On 20:34 Thu 14 Feb, emmanuel segura wrote:
>>
>> man tune2fs
>>
>> -r reserved-blocks-count
>> Set the number of reserved filesystem blocks.
>>
>> be careful with filesystem reserved block, one time i had a production
>> server with / corrupted
>
> I have a very specific use here.
>
> I am using this partition only for 1 time backup of static data, on a backup machine.
>
> I am confused.
>
> I had set the reseved block count to 0 with the
> tune2fs -m0 option.
>
> This is because I dont use this device for system or root. Just data storage.
>
> However I see on the system currently (after only doing tune2fs -m0)
>
> 1. File system features of resize_inode
> 2. Reserved block count 0
> 3. Reserved GDT blocks 1002
>
> what is the idea here of tune2fs -r?
> It says currently that reserved block count is 0.
>
> Should I want to get rid f the GDT blocks?
> Are they the only culprit remaining?
> Are they only used for resizing?
> I will not need to resize once I do my full data backup to this partition.
>
> I am confused because I don't understand the -r option vs the -m 0 option.
>
> According to the following comment from Theodore Tso author of ext2/3/4
>
> http://www.redhat.com/archives/ext3-users/2006-May/msg00008.html
>
> "
>> 1) what does the "Reserved GDT blocks" mean? and what
>> are its functions and purposes?
>
> It means that blocks have been reserved in order to allow on-line
> resizing. The filesystem will also have "resize_inode" in the
> filesystem features line reported by dumpe2fs. This is most useful if
> the filesystem has been created on a Logical Volume managed by an LVM
> system so that when the LV is expanded, the filesystem can take
> advantage of the new disk space without needing to unmount the
> filesystem first.
>
> Filesystems that don't have this set can of course still be resized
> off-line using resize2fs.
> "
>
> I want to understand. Does the -r option turn off the reside_inode reserved space?? what number to put after -r?
> Is that what I want to do?
> Are there any good online references to the next step to get back space, if it is safe to do?
The "-m" option of mkfs.ext3 and the "-r" option of tune2fs are the
same and they're used to set aside space for root and root-owned
processes.
GDT blocks are used for online resizing but as Tso says you can resize
offline without them.
You can use "-O ^resize_inode" to unset this option.
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