On 21/09/16 09:06, Ramon Hofer wrote:
Thank you very much for your answer, Wol!
On Tue, 20 Sep 2016 22:52:00 +0100
Wols Lists <antlists@xxxxxxxxxxxxxxx> wrote:
On 20/09/16 20:34, Ramon Hofer wrote:
I am using 4 TB WD red to replace the 1.5 TB disks.
Do you think this could work?
Are there any pitfalls?
Should I unmount the array to perform all these steps? It might be
safer since there is no redundancy during the replacement?
I just wanted to check first before making any mistakes. Instead of
maybe afterwards asking for help recovering my data :-P
I don't quite understand what you are doing, but ...
Sorry I forgot to mention some things.
I have a linear md0 containing four raid5 (md[1234]) to which XFS is
stripe aligned due to the performance. [1], [2]
The case for my home media server is a Norco [3] with 20 slots. Four are
dedicated to MythTV.
4 x 4 are in md0.
I want to replace the four 1.5 TB disks with 4 TB to have more
space.
On the four 4 TB disks I create two partitions (1.5 TB and 2.5 TB).
Each old 1.5 TB disk gets replaced with the partition on the 4 TB
disks. From the 2.5 TB of each of the four 4TB disks I create a new
RAID5 (md5) and add this to the linear md0. At the end I expand the
file system.
Assuming that you are replacing the four disks that are in the RAID5
array which is at the "end" of your linear raid0, then you don't
actually need to create two partitions at all. Just replace the four
drives (dd from source to destination while offline). When complete, (if
they are partitioned, delete/re-create the single partition to fill the
drive), grow the RAID5 array to fill the new drives, then grow the md0
to take the rest of the RAID5 space onto the end of the drive, then grow
your filesystem/etc.
The other way to do it is just shut the machine down, remove all
drives except one and put a new big drive in. Boot from a rescue CD,
partition the new drive and dd the old partitions to the new drive.
Again rinse and repeat for all four drives, and then put all four new
drives in the system and reboot. At which point you can expand all the
filesystems/raids to use all the space available. This *shouldn't* be
a risky operation. Indeed, if you're going to shut the array down,
this is probably the simplest and safest option.
So you suggest to dd the 1.5 TB disks to the 1.5 TB
partition on the 4 TB disks instead of just let mdadm rebuild the
array?
Agreed, possibly faster, definitely safer if you value your data.
Can I just do:
sudo dd if=/dev/sde of=/dev/sdf1
Depends, is the existing sde partitioned? Make extra sure you pair up
each source/destination drive, etc...
Assuming sde is the old 1.5 TB disk and sdf1 is the 1.5 TB partition on
the new 4 TB disk.
Can I be sure that mdadm recognizes the partitions correctly as the
replacement for the old disks?
mdadm will use the content of the drive/partition to work out what
belongs in/to what array, so it should be fine. However, its a great
idea to keep the four old drives aside until you are sure everything is
working properly (another advantage to avoid replacing one at a time...)
Note that this advice might mess with your "performance tuning", I don't
know enough about that side of things to comment further.
Regards,
Adam
--
Adam Goryachev Website Managers www.websitemanagers.com.au
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