raid5 equivalent growing and shrinking posible?

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raid5 equivalent growing and shrinking posible?

Postby creepwood » 2017-07-02 15:20

I'm wondering what methods are available if any there is to grow and shrink raid5 (or equivalent).

In this new world of software raids the possibilities are much better than back in the days. I've been using lvm for my data drives on my debian jessie home server. Now I'm considering instead of having a 3 partition mirror for the data that I absolutely can not loose and then the rest of the partition essentially just one logical volume. I have 5 identical drives (WD RED 3TB). Some still with data on them so I will not be able to add all the drives from start. I'm making sure that I will have 3 drives available from start. are there any good ways of doing this? In lvm there seem to be something called raid5_ls and then mdadm. I haven't used mdadm at all so if it's available in lvm I would feel much more secure.

It's essential that I will be able to shrink it in the future and not get stuck with something so big I won't be able to handle it.

Edit: Oh, And I'm very novice in the linux world
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Re: raid5 equivalent growing and shrinking posible?

Postby steve_v » 2017-07-02 21:36

creepwood wrote:I'm wondering what methods are available if any there is to grow and shrink raid5 (or equivalent).

MDRAID can be resized, check the documentation.

raid5

data that I absolutely can not loose

Mutually exclusive IME. RAID is not a backup, and RAID5 especially so.

I haven't used mdadm at all so if it's available in lvm I would feel much more secure.
MDADM and LVM operate on different layers, the usual solution is LVM on top of an MDRAID array.

It's essential that I will be able to shrink it in the future and not get stuck with something so big I won't be able to handle it.
Shrink how? Remove drives? IIRC it's possible within the same RAID level if you have sufficient redundancy, but going from, say, a RAID5 to a mirror is a teardown and rebuild.
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Re: raid5 equivalent growing and shrinking posible?

Postby creepwood » 2017-07-03 13:24

steve_v wrote:Shrink how? Remove drives? IIRC it's possible within the same RAID level if you have sufficient redundancy, but going from, say, a RAID5 to a mirror is a teardown and rebuild.


Thank you for your answer, I'm referring to dropping a drive from maybe 5 to 4 drives in a raid5
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Re: raid5 equivalent growing and shrinking posible?

Postby steve_v » 2017-07-04 09:56

creepwood wrote: I'm referring to dropping a drive from maybe 5 to 4 drives in a raid5
The manual says:
Grow

Grow (or shrink) an array, or otherwise reshape it in some way. Currently supported growth options including changing the active size of component devices and changing the number of active devices in Linear and RAID levels 0/1/4/5/6, changing the RAID level between 0, 1, 5, and 6, and between 0 and 10, changing the chunk size and layout for RAID 0,4,5,6, as well as adding or removing a write-intent bitmap.
Which says "yes" to me. But I'd test it first anyway.
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