Re: btrfs raid assurance

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2017-07-25 17:45, Hugo Mills wrote:
> On Tue, Jul 25, 2017 at 11:29:13PM +0200, waxhead wrote:
>>
>>
>> Hugo Mills wrote:
>>>
>>>>>     You can see about the disk usage in different scenarios with the
>>>>> online tool at:
>>>>>
>>>>> http://carfax.org.uk/btrfs-usage/
>>>>>
>>>>>     Hugo.
>>>>>
>> As a side note, have you ever considered making this online tool
>> (that should never go away just for the record) part of btrfs-progs
>> e.g. a proper tool? I use it quite often (at least several timers
>> per. month) and I would love for this to be a visual tool
>> 'btrfs-space-calculator' would be a great name for it I think.
>>
>> Imagine how nice it would be to run....
>>
>> btrfs-space-calculator -mraid1 -draid10 /dev/sda1 /dev/sdb1
>> /dev/sdc2 /dev/sdd2 /dev/sde3 for example and instantly get
>> something similar to my example below (no accuracy intended)
> 
>     It's certainly a thought. I've already got the algorithm written
> up. I'd have to resurrect my C skills, though, and it's a long way
> down my list of things to do. :/
> 
>     Also on the subject of this tool, I'd like to make it so that the
> parameters get set in the URL, so that people can copy-paste the URL
> of the settings they've got into IRC for discussion. However, that
> would involve doing more JavaScript, which is possibly even lower down
> my list of things to do than starting doing C again...
Is the core logic posted somewhere?  Because if I have some time, I 
might write up a quick Python script to do this locally (it may not be 
as tightly integrated with the regular tools, but I can count on half a 
hand how many distros don't include Python by default).
> 
>     Hugo.
> 
>> d=data
>> m=metadata
>> .=unusable
>>
>> {  500mb} [|ddddd|] /dev/sda1
>> { 3000mb} [|ddddd|mmmmm|mmmmm|mmmmm|mmmmm|mm...|] /dev/sdb1
>> { 3000mb} [|ddddd|mmmmm|mmmmm|mmmmm|mmmmm|mmm..|] /dev/sdc2
>> { 5000mb}
>> [|ddddd|mmmmm|mmmmm|mmmmm|mmmmm|mmmmm|mmmmm|mmmmm|mmmmm|mmmmm|]
>> /dev/sdb1
>> --------
>> {11500mb} Total space
>>
>> usable for data (raid10): 1000mb / 2000mb
>> usable for metadata (raid1): 4500mb / 9000mb
>> unusable: 500mb
>>
>> Of course this would have to change one (if ever) subvolumes can
>> have different raid levels etc, but I would have loved using
>> something like this instead of jumping around carfax abbey (!) at
>> night.
> 
>     The core algorithm for the tool actually works pretty well for
> dealing with different RAID levels, as long as you know how much of
> each kind of data you're going to be using. (Although it's actually
> path-dependent -- write 100 GB of RAID-0 then 100 GB of RAID-1 can
> have different results than if you write them in the opposite order --
> but that's a kind of edge effect).
> 
>     Hugo.
>