Re: [Moosefs-users] Chunk servers and disks per server

[Travis H. <tra...@tr...>]

On 2010-09-08, at 10:59 AM, Kristofer Pettijohn wrote:

> How does MooseFS treat multiple disks on a chunk server?  Does it try to spread the data out in some sort of balance?
> If there are 2 chunk servers, and one has two disks, the other has one disk (so 2 chunk servers, 3 disks total), if there is a goal for a file set to 2, is it possible that the both chunks will be stored on different disks of one chunk server, or is MooseFS smart enough to know to keep them on separate servers?
> 
> Thanks,
> Kris Pettijohn
> 

I believe all of the disks within a chunk server behave to the system as one copy. Within the chunk server  the disks are used as the need arises.  

So in your example, having two chunk servers, when setting the goal for a file to 2, the files will be stored on both chunk servers, but not necessarily utilizing both disks on the one chunk server that has more than one disk in it.

Another thing to consider, in this example, files will only be able to be stored at their desired goal (of 2 here), as long as all of the chunk servers (2 in this case) have room to store new files.  If one chunk server would to become at capacity, while the other chunk server had more space free due to it's second disk, the files would be stored in the remaining space (due to the second disk) on this other chunk server, but would be done so at 'under goal' condition.  The solution to achieve the desired goal for these files might then be to add another disk to the first chunk server, or set up an additional chunk server.

Travis