First some minor clarifications.  A "disk pool" is a collection of (at most) 6 disks within a node.  High-level, Isilon nodes have the following chassis capacities:  - X400, X410 and NL400: 36 disks per chassis - X200: 12 disks per chassis - S200 and S210: 24 disks per chassis  So for example an X400 will have 6 disk pools, an X200 will have 2 disk pools, and an S200 will have 4 disk pools.  You can think about a disk pool as a "fault domain", in the sense that whatever protection policy (e.g. +2:1) is set in OneFS applies at the individual disk pool level.  As an example, consider a 5 node x400 cluster running +2:1, where each node has 6 disk pools (each disk pool contains 6 disks from each node, so in this example of a 5 node cluster, each disk pool contains 6 x 5 = 30 disks in total).  On that cluster, you could theoretically have 12 simultaneous disk failures, across all the nodes, without risk to data.  For this to be true though, each disk pool could not have more than 2 failures.  So, if there were 2 failures in each of the 6 disk pools (for 12 total failures), all the data in the filesystem would still be available.  To answer your specific questions:  - Case 1: Correct, no data unavailable situation.  Each node pool at +2:1 can sustain a node loss.  -Case 2: Correct, no data unavailability, as explained above.  As long as the failures are spread out amongst the disk pools, and the per-disk pool failure number does not exceed the protection policy, the filesystem is completely available.
hi there ...  With OneFS 7.0~what is the ptotection level for listed below ? Considering protection level is works by Disk Pools ... ( Ibelieve .. )  System Using X-node and S-node Cluster  Protection ;evel : N+1:2  X-node pool has 4 disk pools S-Node pool has 2 diks pools  Case1 . 1 node failure @ x-node 1 node failure [NAME]-node --> as n+2:1 Allows to fail one node per node pool , this case does not create DL .... Correct ?   Case2 4disk failure( 2 disk failure by each Disk Pool )  [NAME]-node 8disk failyre ( 2 disk failure by each disk Pool) [NAME]-NOde --> As N+1:2 allows 2disk failue within by per disk pool, ( ??) above failure situation does not create DL ?  thanks ! Aya   
Protection for failure