Looking for the best way to proceed... (advice needed)

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Gerg
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Looking for the best way to proceed... (advice needed)

Unread post by Gerg » Fri Jul 20, 2018 1:59 pm

I run a DS1813+ at home that stores the family files (documents, audio, video, photos,...).
Since the beginning I've been running with 5 drives of 4TB each in a SHR configuration (using ext4 as filesystem).
The volume is full though now so I need to expand.
For expansion I am looking at 8TB drives (WD RED like the existing ones) because those seem to be in the pricing sweet spot.

Question: is what I am thinking of doing here (see below) completely bonkers or is it possible.... ?

Options (that I see):

(1) I have 3 empty bays in my DS1813+ so I can add 3 new 8TB drives. At the moment my 5 drives are in a single volume storage pool but I understand that it is quite easy to change this to 'multi-volume' once I add the extra disks. Now I would like to create a new (second) volume but with btrfs (instead of ext4). My main reason for switching to btrfs is to avoid the scrubbing that I currently need to do at least every once every month and which takes ages (feels like it anyways). The new volume should (just) have enough room so I can copy over the existing data from the existing (old) volume (if not then I'll temporarily remove some stuff from the NAS). The next step in the plan is to remove all the old disks thereby freeing up 5 bays to alow me to expand more easily (by adding more 8TB drives). The problem is that I think I understand that there is no functionality to 'remove' drives from the device. Can someone please confirm this? Is there a way to delete the existing (old) volume and then proceed to remove the drives without DSM going berzerk? In this approach I like the idea that all data is moved to new disks, the existing disks have been running 24/7 for 4 years...

(2) I have 3 empty bays in my DS1813+ so I can add 3 new 8TB drives. This time though I could just add them to the existing volume... this should surely work but forces me to stay with ext4. I do not possesss the knowledge to assess how much of a disadvantage (or advantage...) that could be. Further (future!) expansion now requires to replace old 4TB drives by 8TB ones.

(3) I could start to replace each of my existing 4TB drives by an 8TB one. I understand this should be done one at a time (with a repair step every time a drive is replaced). I fear this approach because of the time that wil be spernt repairing the volumes. I do not see any clear advantage with this approach...

I prefer option (1) but do not know if it is even possible...
Any advice/insight from people more knowledgable on this subject would be much appreciated...
Thank you in advance.

Gerrit

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Re: Looking for the best way to proceed... (advice needed)

Unread post by coop777 » Fri Jul 20, 2018 7:20 pm

So it looks like you have ~14 - 15 TB of data. What I would do at this point is create an SHR1 array with the new 8 TB drives - move all your data to it, then you can simply remove the old volume, remove the old 4 TB disks and then expand your new array with 8TB or higher disks as you need more space.

Gerg
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Re: Looking for the best way to proceed... (advice needed)

Unread post by Gerg » Sat Jul 21, 2018 12:10 pm

coop777 wrote:
Fri Jul 20, 2018 7:20 pm
So it looks like you have ~14 - 15 TB of data. What I would do at this point is create an SHR1 array with the new 8 TB drives - move all your data to it, then you can simply remove the old volume, remove the old 4 TB disks and then expand your new array with 8TB or higher disks as you need more space.
You suggest to "create a new SHR1 array"
=> do I understand you correctly that this means to create a new "Storage Pool" (containing the 3 new 8TB drives)?
=> then I can create a new volume (using btrfs) in this pool
=> then I can copy all my stuff to the new volume
=> great :D

If I understand you correctly it is not a problem to remove the old volume and then to remove the old storage pool.
Is this understanding correct? :?: (it is mostly this kind of reassurance that I am looking for, info on the web is very unclear about this)

Many thanks for your help!
Gerrit

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Re: Looking for the best way to proceed... (advice needed)

Unread post by coop777 » Mon Jul 23, 2018 7:03 pm

The point is to make sure you have your data copied off the old array to the new before you remove it. By creating the new SHR1 array you will have just over the amount of total storage space available on the old with one disk redundant and now expandable as needed.

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Re: Looking for the best way to proceed... (advice needed)

Unread post by Squozen » Tue Jul 24, 2018 10:59 am

You will still need to do scrubbing even with btrfs. :)

Gerg
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Re: Looking for the best way to proceed... (advice needed)

Unread post by Gerg » Thu Jul 26, 2018 12:08 pm

Squozen wrote:
Tue Jul 24, 2018 10:59 am
You will still need to do scrubbing even with btrfs. :)
Thank you for pointing that out (I did not know scrubbing was done both at the raid level and at the file system level).
I suppose btrfs still gives me more reassurance that at the file level my files are OK (or is that also a wrong assumption..).

The 2 things that are still not clear to me (perhaps this is common knowledge...):
  • I will be able to remove the 'old' volume once I have copied all my files
  • I will be able to remove the 'old' storage pool (I am assuming I need to put the new drives in a new storage pool) without problems (once the 'old' volume has been removed of course)...
Thanks again for any info.

Squozen
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Re: Looking for the best way to proceed... (advice needed)

Unread post by Squozen » Thu Jul 26, 2018 1:42 pm

As long as there is a disk in the unit you can remove any volume or storage pool you like (presuming there are no apps installed on it). When you put a new drive in, DSM is installed on a hidden partition and any unwanted disks can be removed.

If I were you I would consider making a 4-drive SHR2 volume given that you're using 8TB drives and rebuild times will be quite long, especially if you're not making backups.

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Re: Looking for the best way to proceed... (advice needed)

Unread post by Gerg » Thu Jul 26, 2018 3:47 pm

Squozen wrote:
Thu Jul 26, 2018 1:42 pm
If I were you I would consider making a 4-drive SHR2 volume given that you're using 8TB drives and rebuild times will be quite long, especially if you're not making backups.
That is indeed an interesting idea but the problem is ... space... :( 3 8TB drives (3 available slots) in SHR2 only give me 8TB of available space and currently there is about 15TB of data on there. I have backups of the most important stuff (family documents & pictures) but not of the full 15TB (too expensive to justify on the family budget)...
Or do you mean I could pull out an extra (4TB) drive from the existing set (making it 'damaged') and replace that one too with an 8TB drive (that would give me about the same space in SHR2 as I have now with my 4x4TB drives in SHR)?

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Re: Looking for the best way to proceed... (advice needed)

Unread post by Squozen » Fri Jul 27, 2018 10:09 am

You cannot create a 3-disk SHR2 array, of course. So you'd need to backup as much critical data as you can and then deliberately degrade the array in order to create the new one. Immediately move everything across while the Synology is still running the parity check on the new array and then you can destroy the degraded array once you're satisfied that everything has been moved.

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