planning general storage capacity for y fs

[Dolev Raviv]

>On Sun, Apr 26, 2015 at 1:14 PM, Dolev Raviv <draviv at codeaurora.org> wrote:
>> Hi,
>> I'm looking for guidelines for planning storage capacity. I understand 
>> it strongly depended on the usage type.
>> I want to know at what point storage fullness is effecting performance 
>> in a standard read/write partition. Do different File Systems 
>> (UBIFS/EXT4) have different full-free ratio?
>> What about read only fs? Can I plan less free space in such cases?
>>
>> I'll appreciate any input on this, for UBIFS specific and fs in general.
>
>Not sure if I got your question.
>You want to know how filesystems in general behave when they run out of free space?
>The general answer is that they need more effort to find free space.
>
>In case of UBIFS you also have to think of the garbage collector.
>See http://www.linux-mtd.infradead.org/doc/ubifs.html
>At the end of the day you'll have to run benchmarks on your own to find out how a specific filesystem behaves on your workload...
>

Thanks Richard!
Let me rephrase the question: In the past I knew there was a rule of thumb, 'leave free 30% of the storage space'. Nowadays I couldn't find any reference to this.
I was wondering, is there a known point in UBIFS (or ext4), where leaving less free storage space, that performance is dropping? Maybe a ratio of free-occupied is not the right way to look at it, but to leave a certain size free (e.g. 50MB)?

Thanks,
Dolev
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