Author Topic: Issues Expanding Array  (Read 4071 times)

Offline snown

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Issues Expanding Array
« on: August 25, 2015, 09:43:05 am »
I am using tRAID on Linux. I've added an additional 4TB drive, as well as
upgrading a 3TB drive to a 4TB one. My PPU is 4TB.

However, my Pool volume doesn't seem to be getting bigger. I've gone
through "Verify+", "Verify Sync", and complete removal of the RAID
configuration as well as unregistering all the disks are re-registering
them. Nothing I do seems to expand the size of my pool.

What am I doing wrong with expansion?

Thanks!

Offline Brahim

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Re: Issues Expanding Array
« Reply #1 on: August 25, 2015, 10:47:54 am »
Was the added disk previously formatted with a partition label as required?

Offline snown

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Re: Issues Expanding Array
« Reply #2 on: August 25, 2015, 05:28:43 pm »
I believe so. I set it up in the exact same way as I've set up the rest of my drives. Here is a screenshot from gparted (although those file system warnings are new):


Offline Brahim

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Re: Issues Expanding Array
« Reply #3 on: August 25, 2015, 05:57:26 pm »
Well, there is your issue. Format it with a filesystem and label the partition.

http://wiki.flexraid.com/2014/06/22/ultimate-linux-guide-to-transparent-raid/

Offline snown

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Re: Issues Expanding Array
« Reply #4 on: August 25, 2015, 07:46:47 pm »
Ok I'll try that (weird that it didn't take the first time).

What about the drive that replaced the old drive (3TB to 4TB)? The content is there, and it seems to be working, but I did not see an increase in pool size.

Thanks.

Offline Brahim

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Re: Issues Expanding Array
« Reply #5 on: August 25, 2015, 08:04:16 pm »
When you restore a smaller drive to a larger one, the available space remains the same. To fully utilize the larger drive, you will need to format it. This means, you will need to backup the data on the disk, delete the array, format the drive, copy the data back to it, and re-create the array and parity.

Offline snown

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Re: Issues Expanding Array
« Reply #6 on: August 26, 2015, 09:24:13 am »
Oh, bummer. I guess I assumed I would be able to increase the size after the restore, and then recalculate the parity.

So if you're swapping out a failed drive, you have to let the parity restore the failed content onto the new larger drive, then back up that drive, format it, and then start the parity over from scratch? Seems like there should be a way around all those steps.

What happens when you have a Hot Spare that's larger than the failed drive?

Thanks.

Offline Brahim

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Re: Issues Expanding Array
« Reply #7 on: August 26, 2015, 09:40:14 am »
When restoring to a larger disk, the partition is restored faithfully and hence your confusion. The restored partition size on the new disk will be exactly the same as on the old disk. To make use of the remaining space on the larger disk, you normally have to create a second partition on the larger disk above the restored partition.

Don't use the restore process for RAID Expansion. What you need to do is an RAID Contraction first to remove the smaller disk, then outside of the array copy the content of the smaller disk into the larger disk, and then do a RAID Expansion using the larger disk.

So, when you restore to another disk whether the same size or larger, you will get a faithful restoration of the disk (nothing more and nothing less).

Offline snown

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Re: Issues Expanding Array
« Reply #8 on: August 26, 2015, 09:43:41 am »
Interesting, I never thought about creating a second partition. I assume then that the new partition would be treated as a separate drive according to the RAID? In which case if that hard drive dies, and if your RAID is only set up to cover one failure, you would loose some content?

Thanks again for your help and clarification.

Offline Brahim

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Re: Issues Expanding Array
« Reply #9 on: August 26, 2015, 10:00:51 am »
No, technically, you can have multiple partitions and they will all count as one UoR (Unit of Risk).

However, there is a configuration limitation in the Linux implementation in that only one partition per disk is supported. This is unlike on Windows where there is no such restriction.
Which leads back to the fact that you just don't use the restore process to expand. You are supposed to restore to an identical disk. Being able to restore to a larger disk is a bonus, but which should not be viewed as a segue-way to RAID Expansion.

Offline snown

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Re: Issues Expanding Array
« Reply #10 on: August 26, 2015, 10:10:57 am »
Very interesting indeed. Thanks for the detail, I appreciate it.

Offline Brahim

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Re: Issues Expanding Array
« Reply #11 on: August 26, 2015, 11:21:32 am »
Glad I could help.

These additional comments are to help other readers. Note that you can restore to a larger disk even if that disk is larger than your PPU. Here you can easily see how the additional space off the larger disk cannot simply be added to the array as it would be outside of the parity range.
For parity to remain valid, the restored to disk must be restricted to the characteristics of the disk it is replacing.

RAID-F users have an edge in that they can swap and restore to a larger disk, and the full additional usable space of the larger disk will become available to the array. This is only because RAID-F is medium agnostic. It only cares about actual data. Transparent RAID does not have that flexibility.

Offline snown

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Re: Issues Expanding Array
« Reply #12 on: August 26, 2015, 06:23:52 pm »
Hmmm, now I've got the drive backed up to a previously empty drive, but I can't add it as a pass-through disk. It's the same disk as I showed before, but this time it has a ext4 format, and a label.

Any ideas?

Offline Brahim

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Re: Issues Expanding Array
« Reply #13 on: August 26, 2015, 06:33:25 pm »
You don't say much about what issue or error you are encountering.
Did you de-register the disk prior to taking it over? The registration might still be valid. Check that you can query it in the UI and run SMART on it through its registration handle if there.

Offline snown

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Re: Issues Expanding Array
« Reply #14 on: August 26, 2015, 06:40:55 pm »
It is not registered. I'm not sure how to query it as you say. I'm assuming in that case it would show up in the registered disks section?

I meant to include an image with the last post, sorry. This is what I'm seeing:


This is DRU06, or sde1, here's my registered section: