Re: Where to put the journal

[Edward Shishkin <edward@namesys.com>]

Xuân Baldauf wrote:

> Edward Shishkin wrote:
>
>> Vladimir V. Saveliev wrote:
>>
>>> Hello
>>>
>>> Xuân Baldauf wrote:
>>>
>>>> Hello,
>>>>
>>>> I want to setup a Linux software RAID 5 over disks of different 
>>>> speed with reiserfs on top. I know that the journal has to be 
>>>> accessed frequently for comparably small accesses. That's why I'm 
>>>> considering to "offload" the journal onto an extra partition on a 
>>>> faster disk of the RAID set.
>>>>
>>>> Thus, the journal would not be protected by the RAID, but this is 
>>>> not so important for me.
>>>>
>>>> Is this kind of reasoning sane? Would there be any speedup by 
>>>> offloading the journal?
>>>>
>>>
>>
>> Hello.
>> Unfortunately comprehensive results of journal relocation are obsolete
>> as it was done at the beginning of mongo evolution. As I remember there
>> were no any essential speedups. The only result of  journal  
>> relocation that
>> was created by new mongo benchmark can be found here:
>> http://thebsh.namesys.com/benchmarks/journal_relocation_to_NVRAM.html
>
>
> Thank you,
>
> essentially, these numbers say that relocation provided a speedup of 
> about 10% for write. 


Note this is for data logging journal mode (mount option "data=journal")
Edward.

> This surprises me a bit, because I expected a significantly smaller 
> seek count for a write operation. Nevertheless, maybe I should run 
> benchmarks with many small files for myself. :-)
>
>>
>> Edward.
>
>
>
> ciao,
>
> Xuân Baldauf.
>
>>
>>> Person who did some tests on non standard journal is on vacation. He 
>>> is expected to come back today. Maybe he remembers benchmark results,
>>
>>
>
>
>