Re: [gentoo-user] Process to resize ext3 file system at the command line?

[Mark Knecht]

On Thu, Nov 17, 2011 at 9:25 AM, Neil Bothwick <neil@××××××××××.uk> wrote:
> On Thu, 17 Nov 2011 09:01:46 -0800, Mark Knecht wrote:
>
>>    I'm pretty sure I've got the command set right to do the RAID-1 to
>> RAID-5 conversion, but once it's done I believe the file system itself
>> will still be 250GB so I'll need to resize the file system. In the
>> past I've done this with gparted, which seems to work fine, but this
>> time I was considering doing it at the command line. Does anyone know
>> of a good web site that goes through how to do that? I've browsed
>> around and found different pages that talk about it but my reading
>> looks like they all have minor differences which leaves me a bit
>> worried.
>
> Using cfdisk or fdisk, delete the partition and recreate it, USING THE
> SAME START BLOCK at a larger size.
>
> Then "resize2fs /dev/sdwhatever" will resize the filesystem to fill the
> partition.
>
>
>
> --
> Neil Bothwick

Really? Delete the partition? Sounds scary! (But actually makes sense.
The data is still there.)

I'm not sure how this works in the case of a RAID though. Here's the
current partition table for sda where sda6, sdb6 & sdc6 are part of
the RAID-1::

c2stable ~ # fdisk -l /dev/sda

Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x8b45be24

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *          63      112454       56196   83  Linux
/dev/sda2          112455     8514449     4200997+  82  Linux swap / Solaris
/dev/sda3         8594775   113467094    52436160   fd  Linux raid autodetect
/dev/sda4       113467095   976768064   431650485    5  Extended
/dev/sda5       113467158   218339414    52436128+  fd  Linux raid autodetect
/dev/sda6       481933935   976768064   247417065   83  Linux
/dev/sda7       218339478   481933871   131797197   fd  Linux raid autodetect

Partition table entries are not in disk order
c2stable ~ #

It's not that I want to change the partition size of the 3 pieces of
the RAID-1, it's that after I convert the RAID-1 to RAID-5 I want it
to be 500GB.


I asked some questions on the Linux RAID list and putting together
info from a couple of people here's how I'm thinking I proceed with
the conversion:

1) First, fail one disk and clean it up for later:

umount /dev/md6
mdadm --stop /dev/md6
mdadm /dev/md6 --fail /dev/sdc6 --remove /dev/sdc6
mdadm --zero-superblock /dev/sdc6

At this point the RAID-1 is still 3-drives but one is marked 'failed'.
The failed drive is at this point like a new drive as it has no
superblock. (I think...)

2) Now I convert the 3-drive RAID1 to a 2-drive RAID-1:

mdadm --grow /dev/md6 --raid-devices=2

3) Create a 2-drive RAID-5:

mdadm has an 'instantaneous' conversion of RAID-1 to RAID-5 for the
2-drive case because parity of a single drive is just the data itself.
/dev/sdb6 is now 'parity' instead of 'data'.

mdadm /dev/md6 --grow --level=5

4) Add a 3rd drive to the RAID-5:

mdadm /dev/md6 --add /dev/sdc6
mdadm /dev/md6 --grow --raid-devices=3



At this point I was told:

"Now, resize your filesystem to use the additional space."

So, if at this point the end-block of sda6 isn't 976768064 but, let's
say, 700000000 because mdadm set it to something new, then using your
suggestion I guess I'd set it back to 976768064? I'm not comfortable
however that if I do that that whatever is out there beyond 700000000
is really formatted as ext3 and 'empty' as I don't know what the mdadm
conversion has done to it.


Thanks,
Mark