PanFS allows users to specify the layout of a file at file-creation time. Layout information includes the number of StorageBlades (SB) across which the data is stored, the number of SBs across which a parity stripe is written, and the number of consecutive stripes that are placed on the same set of SBs. The panfs_layout_* hints are only used if supplied at file-creation time.
PanFS supports the ``concurrent write'' (CW) mode, where groups of cooperating clients can disable the PanFS consistency mechanisms and use their own consistency protocol. Clients participating in concurrent write mode use application specific information to improve performance while maintaining file consistency. All clients accessing the file(s) must enable concurrent write mode. If any client does not enable concurrent write mode, then the PanFS consistency protocol will be invoked. Once a file is opened in CW mode on a machine, attempts to open a file in non-CW mode will fail with EACCES. If a file is already opened in non-CW mode, attempts to open the file in CW mode will fail with EACCES. The following hint is used to enable concurrent write mode.
Below is an example PanFS layout using the following parameters:
- panfs_layout_type = 3 - panfs_layout_total_num_comps = 100 - panfs_layout_parity_stripe_width = 10 - panfs_layout_parity_stripe_depth = 8 - panfs_layout_visit_policy = 1 Parity Stripe Group 1 Parity Stripe Group 2 . . . Parity Stripe Group 10 ---------------------- ---------------------- -------------------- SB1 SB2 ... SB10 SB11 SB12 ... SB20 ... SB91 SB92 ... SB100 ----------------------- ----------------------- --------------------- D1 D2 ... D10 D91 D92 ... D100 D181 D182 ... D190 D11 D12 D20 D101 D102 D110 D191 D192 D193 D21 D22 D30 . . . . . . D31 D32 D40 D41 D42 D50 D51 D52 D60 D61 D62 D70 D71 D72 D80 D81 D82 D90 D171 D172 D180 D261 D262 D270 D271 D272 D273 . . . . . . ...
Rob Latham 2016-08-01