Specifications

5102ch02.fm Draft Document for Review May 12, 2014 12:46 pm
56 IBM Power System S822 Technical Overview and Introduction
slots. However cache power protection hardware covers one PCIe x8 slot (P1-C9). Patented
Active/Active configurations with at least two arrays is supported.
The write cache, responsible for increasing write performance by caching data before it is
written do the physical disks, can have its data compression capabilities activated, providing
up to 7.2 GB effective cache capacity. The write cache contents are protected against power
loss with flash memory and super capacitors removing the need for battery maintenance.
The high performance SAS controllers provide RAID 0, RAID 5, RAID 6 and RAID 10 support
and its EasyTier variations (RAID 5T2, RAID 6T2, RAID 10T2) provided the server has both
HDDs and SSDs installed.
Easy Tier function is supported so the dual controllers can automatically move hot data to
attached SSD and cold data to attached HDD for AIX/Linux/VIOS environments. If a EXP24S
SFF Gen2-bay Drawer (#5887) is attached to the adapters, Easy Tier funcionality is also
extended to the disks on this drawer. To learn more about Easy Tier funcionality read 2.6.2,
“Easy Tier” on page 57.
Table 2-19 lists the RAID support configurations by the storage backplane options.
Table 2-19 RAID support configurations
AIX and Linux can use disk drives that are formatted with 512-byte blocks when being
mirrored by the operating system. These disk drives must be reformatted to 528-byte sectors
when used in RAID arrays. Although a small percentage of the drive's capacity is lost,
additional data protection such as ECC and bad block detection is gained in this reformatting.
For example, a 300 GB disk drive, when reformatted, provides approximately 283 GB.
Solid-state drives are always formatted with 528 byte sectors.
Supported RAID functions
Base hardware supports RAID 0, 5, 6, and 10. When additional features are configured, the
server supports hardware RAID 0, 5, 6, 10, 5T2, 6T2 and 10T2:
򐂰 RAID 0 provides striping for performance, but does not offer any fault tolerance.
The failure of a single drive results in the loss of all data on the array. This version of RAID
increases I/O bandwidth by simultaneously accessing multiple data paths.
򐂰 RAID 5 uses block-level data striping with distributed parity.
RAID RAID 5 stripes both data and parity information across three or more drives. Fault
tolerance is maintained by ensuring that the parity information for any given block of data
is placed on a drive separate from those used to store the data itself. This version of RAID
provides data resiliency in the case of a single drive failing in a RAID 5 array.
򐂰 RAID 6 uses block-level data striping with dual distributed parity.
RAID 6 is the same as RAID 5 except that it uses a second level of independently
calculated and distributed parity information for additional fault tolerance. RAID 6
configuration requires N+2 drives to accommodate the additional parity data, making it
less cost effective than RAID 5 for equivalent storage capacity. This version of RAID
provides data resiliency in the case of one or two drives failing in a RAID 6 array. It is
Storage
backplane
JBOD RAID 0, 5, 6,
and 10
RAID 0, 5, 6 and 10 and
Easy Tier
(RAID 5T2, 6T2, 10T2)
Split
backplane
External SAS
port
#EJ0T Yes Yes No Optional No
#EJ0U Yes Yes Yes No Yes