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List:       linux-raid
Subject:    Re: Replace disks
From:       Wols Lists <antlists () youngman ! org ! uk>
Date:       2018-03-28 14:06:15
Message-ID: 5ABBA157.2020602 () youngman ! org ! uk
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On 28/03/18 09:04, Mateusz Korniak wrote:
> On Tuesday 27 of March 2018 13:49:28 Wols Lists wrote:
> 
>> Very much agreed, although if he can add several new drives physically,
>> I also believe you can replace them at the same time
>>
>> mdadm /dev/mdX --add /dev/sdDX /dev/sdEX --replace /dev/sdSX /dev/sdTX
>>  --with /dev/sdDX /dev/sdEX
> 
> Right, but one has to consider trade-offs of having replacement of disks done 
> faster, or having less impact on performance of array.

And if your array is set up properly, the performance impact should be
the same. If your array is not set up properly, your system will keel
over either way ...
> 
>>> I grow FS on LVM level with online expandable FSs like ext4.
>>
>> Which you can't do just yet ... the new array will be the exact same
>> size as the old one, with a large chunk of unused disk space. 
> 
> After copying partition table, I add new partition(s) on remaining free space 
> of larger disks, create RAID device from them, create PV on that, add it VG, 
> and than I can resize LV with FS as I want.
> 
> No pvmove/raid grow needed, easier to put smaller disks back, split array over 
> more disks later.
> 
KISS (Keep It Simple, Stupid).

I use three arrays for /, /var, and /home. I think that was a mistake.
In my rebuild, I think I'm going to shrink that to ONE array. I don't
(yet) use LVM, so that will be going in the mix.

Two arrays, two PVs, one VG, all over a bunch of disks raided together
as one, sounds like a complicated mess asking for trouble. And given the
price of disks, why would he want to bring the 500s back in to use? I'm
chucking 1TB disks into my "spare parts bin" as being "too small to
bother with" now. They're the sort of drives I stick into a system I'm
building as a favour to a mate.

Cheers,
Wol

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