Hints for PANFS (Panasas)

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_layout_type Specifies the layout of a file: 2 = RAID0 3 = RAID5 Parity Stripes
panfs_layout_stripe_unit The size of the stripe unit in bytes
panfs_layout_total_num_comps The total number of StorageBlades a file is striped across.
panfs_layout_parity_stripe_width If the layout type is RAID5 Parity Stripes, this hint specifies the number of StorageBlades in a parity stripe.
panfs_layout_parity_stripe_depth If the layout type is RAID5 Parity Stripes, this hint specifies the number of contiguous parity stripes written across the same set of SBs.
panfs_layout_visit_policy If the layout type is RAID5 Parity Stripes, the policy used to determine the parity stripe a given file offset is written to: 1 = Round Robin

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.

panfs_concurrent_write If set to 1 at file open time, the file is opened using the PanFS concurrent write mode flag. Concurrent write mode is not a persistent attribute of the file.

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