When I replace one raid 5 disk with larger one, can I use spare space for single volume?

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pavlosweb
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When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by pavlosweb » Fri Jul 31, 2020 4:20 am

I am in situation when one of 4x3TB disks failed and I am going to replace it. it is worth to buy larger one? For example 6TB and use spare space for creating single Raid 0 volume? i.e Original raid 5 will be same and I will be able to create extra 3TB partition with no data mirroring? In theory it could work but I doubt it is supported by nas.
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Re: When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by OneCD » Fri Jul 31, 2020 4:45 am

pavlosweb wrote:
Fri Jul 31, 2020 4:20 am
In theory it could work but I doubt it is supported by nas.
Correct (and this is an often-asked question). QTS doesn't support using this dead space. :(

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pavlosweb
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Re: When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by pavlosweb » Fri Jul 31, 2020 5:24 am

I thought so. Since it uses sw raid would not be possible to achieve this with mdadm via terminal? May be even do own partitioning in case NAS would allocate all space. Or may be use partition with extra space (if it could be done) and mount it in some shared folder? I think this propably too big hack to handle by NAS and I would probably end with dead space either. Did someone tried something similar?
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Re: When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by OneCD » Fri Jul 31, 2020 5:26 am

pavlosweb wrote:
Fri Jul 31, 2020 5:24 am
I thought so. Since it uses sw raid would not be possible to achieve this with mdadm via terminal?
Yes, but this is unsupported by QTS. There's no-way to know how it would react to finding your manually-allocated space. ;)

If you're willing to risk it, you could try it and see.

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Re: When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by jaysona » Fri Jul 31, 2020 10:52 am

pavlosweb wrote:
Fri Jul 31, 2020 5:24 am
I thought so. Since it uses sw raid would not be possible to achieve this with mdadm via terminal?
....
QTS is constantly checking the volume config and the partition setup of each drive. If you change the partition, QTS will interpret that as a disk change or disk failure and start rebuilding the raid volume.

DROBO and Synology have their version of hybrid raid that let you use different sized drives.
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pavlosweb
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Re: When I replace one raid 5 disk with larger one, can I use spare space for single volume?

Post by pavlosweb » Fri Jul 31, 2020 1:25 pm

On second thought I think utilizing dead space is not good idea at all. If there was 2 partitions one for raid 5 a and second one for raid 0. If both partitions would have high traffic it could cause performace slowdown for raid 5 array since one disk would have 100% utilization while others not. May be this is good explanations why to avoid this approach.
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