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FC write policy?
Posted: Mon Nov 08, 2010 12:53 pm
by Bjameson
I think I have a pretty good idea how FC caches its write data. But just to make sure, could you please answer this:
Suppose I have 256MB of L1 and 3GB of L2 to hidden memory. Write delay is set to 300 secs.
I create a 1GB file and immediately delete it again. How will FC handle this?
- FC eventually writes the entire 1GB to disk, followed by the delete.
- FC is smart enough to delete the file from the cache, thus preventing writes to disk altogether.
I'd be very interested to know for sure.
Thanks.
Re: FC write policy?
Posted: Tue Nov 09, 2010 3:54 am
by Support
Hi Bjameson,
Currently FC is not smart enough.
So the answer is this one,
Bjameson wrote:FC eventually writes the entire 1GB to disk, followed by the delete.
Re: FC write policy?
Posted: Tue Nov 09, 2010 10:28 am
by Christodoulosk
What happens when a file is on the cache and before it is writen in the disk the file changed?
Is the writen file on the disk the changed one?
Sorry for my English
Re: FC write policy?
Posted: Thu Nov 11, 2010 2:44 am
by Support
Christodoulosk wrote:What happens when a file is on the cache and before it is writen in the disk the file changed?
Is the writen file on the disk the changed one?
Yes, the data written to the disk is always the latest in the cahce.
Re: FC write policy?
Posted: Fri Nov 12, 2010 10:56 am
by Christodoulosk
So it is correct to asume that the total writen data on the real disk is fewer when the FancyCache is on. ?
Re: FC write policy?
Posted: Mon Nov 15, 2010 7:17 am
by Support
theoretically it is. But because of the program implementation limit, sometimes it isn't.
Re: FC write policy?
Posted: Thu Dec 30, 2010 2:46 am
by Support
Now the write amplification bug has been fixed in version 0.4.1. So the total written data to the real disk is fewer if defer write is on.
Christodoulosk wrote:So it is correct to asume that the total writen data on the real disk is fewer when the FancyCache is on. ?