Re: Removing drives

[Michael Evans <mjevans1983@gmail.com>]

On Fri, Mar 5, 2010 at 8:51 PM, Timothy D. Lenz <tlenz@vorgon.com> wrote:
>
>
> On 3/5/2010 1:22 PM, Michael Evans wrote:
>>
>> On Fri, Mar 5, 2010 at 11:00 AM, Timothy D. Lenz<tlenz@vorgon.com>  wrote:
>>>
>>> Current setup, 3 500gb sata drives, each with 3 partitions.
>>> The first partition of each drive make up raid1 md0 boot and most
>>> software
>>> The next partition of each drive make up raid1 md1 swap
>>> The 3rd partition of each drive make up raid5 md2 main data storage
>>>
>>> There is also a 40gb ide drive with 2 partitions, boot/software and swap.
>>> It
>>> was used for install and setup. But I never got boot changed over to md0.
>>> So
>>> currently md0 is not in use. md0 and md2 are mounted to folders on the
>>> 40gb
>>> so a precopy to md0 could be made before booting with a cd and copying
>>> what
>>> ever is left that needs coping. and to use md2.
>>>
>>> Current
>>> # /etc/fstab: static file system information.
>>> #
>>> #<file system>  <mount point>     <type>    <options>         <dump>
>>>  <pass>
>>> proc            /proc           proc    defaults        0       0
>>> /dev/hda1       /               ext3    defaults,errors=remount-ro 0
>>>   1
>>> /dev/hda5       none            swap    sw              0       0
>>> /dev/md0        /mnt/md0        ext3    defaults        0       0
>>> /dev/md2        /mnt/md2        ext3    defaults        0       0
>>> /dev/hdb        /media/cdrom0   udf,iso9660 user,noauto     0       0
>>> /dev/fd0        /media/floppy0  auto    rw,user,noauto  0       0
>>>
>>> I want to change md0 and md1 from 3 drive mirriors to 2 drive mirrors.
>>>
>>> Finish changing over to booting from md0, move swap to md1 and move the
>>> mount point for md2 to md0
>>>
>>> Remove the the ide drive to free up space for the 4th 500gb drive.
>>>
>>> Copy md2 over to the new 500gb temparally.
>>>
>>> Get rid of the current md2 freeing up the 3rd drive since it was already
>>> taken out of the mirrors above.
>>>
>>> Make a new md2 raid1 with the remaining space of the first 2 sata drives.
>>>
>>> Move the data from the 4th drive back to the new md2
>>>
>>> Repartition the 3rd drive to 1 partition same as the 4th drive.
>>>
>>> Make raid1 md3 from the 3rd and 4th drives.
>>>
>>> It's the steps/commands to change md0 and md1 from 3 drive mirrors to 2
>>> drive mirrors that I'm not sure about. Though now looking at fstab I see
>>> I
>>> never even switched over the swap. So I guess, those to arrays would be
>>> rebuilt. So it's more how to do that without messing with md2.
>>>
>>> The computer is still on grub1. I haven't updated it it.
>>>
>>
>> So you have:
>>
>> [3-devices]
>> Raid 1: Unused
>> Raid 1: Unused
>> Raid 5: Used - 3 disks
>>
>> [1-device]
>> Boot + swap
>>
>> Just swapoff the raid-swap you want to re-create, then:
>> mdadm -S /dev/md(swap)
>> mdadm -S /dev/md(boot)
>> mdadm --zero-superblock /dev/devices in those arrays
>>
>> Repartition those two areas of the disks as necessary.
>>
>> Create new boot and swap partitions.
>> For boot make SURE you use either -e 0.90 OR -e 1.0 .   Given the
>> nature of /boot I'd say use -e 0.90 on it.
>> For everything else, including swap use -e 1.1 and optionally
>> write-intent bitmaps.
>>
>> At this point you should be able to move /boot and your swap off of
>> the 40gb drive; just remember to re-install grub and that your BIOS
>> likely sets the boot drive as bios-drive 0 regardless of which SDA/HDA
>> linux sees it as.  This is what the device.map file is used to tell
>> grub.
>>
>>
>> I lost exactly what you wanted the result to look like amid a long
>> list of steps you /thought/ you needed to make to get there and
>> references to md numbers that only have meaning to you.  However it
>> seems that you were mostly stuck getting to this point, so you might
>> be able to determine a plan using the data you've yet to share with
>> the rest of us with that 40gb drive out of the equation.
>>
>> Remember that you can't reshape raid10 yet, but you can start raid10
>> with 'missing' devices (and add in the spares later).
>>
>
> can't make it much clearer, and I don't know where you got raid10 from.
>
> ARRAY /dev/md0 level=raid1 num-devices=3
> UUID=e4926be6:8d6f08e5:0ab6b006:621c4ec0
> ARRAY /dev/md1 level=raid1 num-devices=3
> UUID=eac96451:66efa3ab:0ab6b006:621c4ec0
> ARRAY /dev/md2 level=raid5 num-devices=3
> UUID=a7ed721e:04b10ab6:0ab6b006:621c4ec0
>
> md 0 and 1 I want to change to 2 deivces.
> Then get it booting from md0 which I think I know how to do as I got another
> computer working that way. Then I can dump the ide drive making room for
> another 500gb sata. It will be used to store the data from md2 while md2 is
> remade from a 3 device raid5 to a 2 device raid1. This frees up a drive
> giving me 2 500gb drives to make another 2 device raid1. Its the seperating
> out 1 device from each of the current raid1's, md0 and md1 that I was asking
> about.
>

That was concise enough to be worth reading through to get your desired result.

I already told you how to do the safe portion of your last operation.

Actually, I can see one benefit from two raid 1s over raid10; you
could stripe them using LVM and for very little extra cost have a lot
more flexibility.

After you've followed my last email to get the system booting off your
raid devices, you can replace the 40 with a 500, and then use the
/new/ 500 to start a raid 1 with one device set as 'missing'.
StartSlower but totally safe way:

However what I'd do if I were you is get everything I could off of the
40gb drive; it would only take 10 DVDs at worse case; presuming it
won't fit within ~500gb.

1) Duplicate all your data from the raid5 on to the single disk in a
raid 1 + missing configuration.
* you now have 1 copy with parity, and 1 copy waiting for mirroring.
(two copies and some parity)

2) Fail one of the partitions from the raid5, --zero superblock it.
* you now have 1 copy without parity, and 1 copy waiting for
mirroring, and one free drive. (two copies)

3) --add the previous parity partition as part of the mirror set; IT
MUST BE >= the size of the other partition in that mirror.
* You have 1 copy without parity, 1 full copy being mirrored in to two copies.

4) WAIT for the mirroring operation to finish.

5) Optionally 'check' the mirror copy.
* You now have 1 copy without parity, 1 fully mirrored copy (3 copies
of your data)

6) With a fully safe copy of your data, and two partitions you can
start a wider range of procedures.

You could create two more raid 1 + missing arrays
setup LVM with striping across them
copy your data over in to one logical volume
++THEN AGAIN in to a second logical volume
(Manually creating two copies of your data; this won't protect against
drive failure but it will protect against individual failed sectors,
which may be good enough.)
Finally one at a time fail out members of the intact raid1 set and add
them to the new raid 1s.


Or probably proceed through other ideas; though none seems as
appealing to me as what I just wrote; 4 drives isn't enough to
seriously consider raid 5 or 6, and with the size of the drives you'd
really be better off with going for raid 6, which is much slower and
only slightly less risky than raid 1 + striping via LVM.
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