Hi this is a query about storage pool history to try and profile expected theoretical IO.

Background,

I understand that flare attempts to allocate disks in blocks of 5 and that therefore depending on history of a storage pool, the number of spindles data is on depends on the history of the storage pool. An example may show my understanding here.

So we allocate a raid 5 storage pool with 5 disks. In this case there is a fairly straight mapping between the storage pool and the private raid group within this.

If we allocate say 10 GB ( Lets call this LUN A ). Then data is striped across 5 disks.

So now we expand the storage pool by 5 disks. Existing data is not restriped. If we allocate a second LUN ( Lets call this LUN B ) with 10 GB, data in allocated in segments of 1 GB so is striped across 10 disks.

So in calculating performance, ignoring fast for a moment,

LUN A performance is 5 x disk IOPS, with write penelty of 4.

LUN B performans is 10 x disk IOPS, with write penelty of 4.

So if the above understanding is correct, we need to know the layout of the 1 GB segments to get an understanding of theoretical IOPS as simply saying its a 10 disk storage pool is misleading.

So my questions are;

1. Is the above simplistic understanding correct ?

2.. If it is correct, is there a way of knowing the segment layout to calculate the theoretical IOPs for a LUN ?

3. I have deliberatly left out FAST, as I do not know how to model this, and thoughts ? i.e. if I have a pool with 3 different disk performance characteristics, can I model what to expect in terms of performance ?