[OpenAFS] 1.3.x memcache performance

[Horst Birthelmer]

On Dec 27, 2004, at 6:20 PM, Andrej Filipcic wrote:

> On Monday 27 December 2004 17:39, Kris Van Hees wrote:
>> On Mon, Dec 27, 2004 at 05:28:14PM +0100, Andrej Filipcic wrote:
>>>>> On gigabit network, the copy speed with memcache is never larger 
>>>>> than
>>>>> 20
>>>>> mbyte/s, with disk cache it can go up to 70 mbyte/s.
>>>
>>> Well, it is not actually performance. dd if=/dev/zero to afs space
>>> transfer reaches something like that. This is of course a peak 
>>> number.
>>> Half of time data is written to a local disk cache with no network
>>> activity, so on average, the transfer would be 30-40 MB/s. AFS read 
>>> speed
>>> is between 10-20 MB/s.
>>>
>>> New memcache parameters give similar write transfer now (~60 MB/s on
>>> average).
>>
>> So basically, you are measuring a combination of how fast you can 
>> write to
>> your cache, together with how fast the AFS client can flush the data 
>> from
>> the cache to the server.  Do you have writebehind turned on or off on 
>> your
>> AFS client?  If writebehind is allowed, then you only measure writing 
>> to
>> the cache + part of the flushing to the server (since flushbehind 
>> allows
>> the close() system call to return before the entire file has been 
>> flushed
>> to the server).
>
> No such tuning. I wanted to know why memcache client was so slow as 
> compared
> to diskcache (kde login to afs home, untar, ...) when the disk load on 
> the
> server was very high. The default memcache settings are obviously not 
> too
> usefull...

That depends on your network, the sizes of your files and the nature of 
the file access.
But that's always the problem with default values on caches. ;-)

I'm not very sure how fast your AFS client is supposed to be...

Horst