IBM N Series, Implementation Manual

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12 Understanding storage provided by native disk shelves
See “ Supported disk types and disk shelves ” on page 10 for details about which
disks and disk shelves that the gateway supports. For information about the
number of disk shelves and disk types that you can connect to a controller, see the
information provided for N series storage systems.
RAID types
supported
Gateway RAID support is different for native disk shelves and array LUNs, as
follows.
RAID types supported by native disk shelves:
For native disk shelves,
Data ONTAP organizes disks into RAID groups, which are collections of data
and parity disks, to provide parity protection. Data ONTAP supports the
following RAID types on native disks:
◆
RAID4 technology: Within its RAID groups, Data ONTAP allots a single
disk for holding parity data, which ensures against data loss due to a single
disk failure within a group.
◆
RAID-DP™ technology (DP for double-parity): RAID-DP provides a higher
level of RAID protection for Data ONTAP aggregates. Within its RAID
groups, Data ONTAP allots one disk for holding parity data and one disk for
holding double-parity data. Double-parity protection ensures against data
loss due to a double disk failure within a group.
RAID types supported for array LUNs:
For third-party storage arrays, the
gateway stripes across array LUNs using RAID0, thereby maximizing
performance because it is using more spindles. A gateway does not provide disk
protection for storage from third-party storage arrays. The reason is that the array
LUNs are already protected with the redundancy provided by the various RAID
levels on the storage arrays.
Note
Do not use RAID0 on storage arrays for array LUNs for gateways: you do not
have redundancy for your data if you use RAID0.
Checksum type of a
native disk All new systems running Data ONTAP use block checksum (BCS) disks. FC
BCS disks are formatted with 520 bytes per sector. Of those 520 bytes, 512 are
available for data, while 8 bytes are used by RAID for the checksum. SATA BCS
disks are formatted with 512 bytes per sector and use one sector for the checksum
for every eight data sectors.