Re: SSD and non-SSD Suitability

[Gordan Bobic <gordan-UpbECiGlrmGsTnJN9+BGXg@public.gmane.org>]

David Arendt wrote:

>>>>> 4) As the data gets expired, and snapshots get deleted, this will 
>>>>> inevitably lead to fragmentation, which will de-linearize writes as they 
>>>>> have to go into whatever holes are available in the data. How does this 
>>>>> affect nilfs write performance?
>>>>>         
>>>> For now, my understanding, nilfs garbage collector moves the live (in use)
>>>> blocks to the end of logs, so holes are not created (it is correct?).
>>>> However, it leads another issue that garbage collector process, which is
>>>> nilfs_cleanerd, will consume the I/O.  This is major I/O performance
>>>> bottle neck current implementation.
>>>>       
>>> Since this moves files, it sounds like this could be a major issue for 
>>> flash media since it unnecessarily creates additional writes. Can this 
>>> be suppressed?
>>>     
>> You can simply kill the nilfs_clearnerd after you mount the nilfs partition.
>>   
> If you use the latest nilfs_utils, killing nilfs_cleanerd is no longer
> necessary. You can use mount -o nogc. This will not start
> nilfs_cleanerd. Another possibility is to let nilfs_cleanerd start and
> tweak min_free_segments and max_free_segments so that cleanerd will only
> do cleaning if necessary.

What about making the gc run only if the disk has been idle for, say, 
20ms, unless min_free_segments is reached?

Gordan
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