Specifications
Chapter 2. Architecture and technical overview 57
Draft Document for Review May 12, 2014 12:46 pm 5102ch02.fm
designed when working with large capacity disks, once it allows to sustain data parity
during the rebuild process.
RAID 10 is also known as a striped set of mirrored arrays.
It is a combination of RAID 0 and RAID 1. A RAID 0 stripe set of the data is created across
a two-disk array for performance benefits. A duplicate of the first stripe set is then mirrored
on another two-disk array for fault tolerance. This version of RAID provides data resiliency
in the case of a single drive failure and may provide resiliency for multiple drive failures.
RAID 5T2, RAID 6T2 and RAID 10T2 are the same RAIDs as defined above but with
EasyTier enabled. It requires that both types of disks exists on the system under the same
controller (HDDs and SSDs) and that both are configured under the same RAID type.
2.6.2 Easy Tier
With the standard SAS adapter (#EJ0T) the server can handle both HDDs and SSDs
attached to its storage backplane as long as they are on separate arrays.
The High Performance RAID adapters (#EJ0U) has the ability to handle both types of storage
in two different ways:
Separate Arrays: SSDs and HDDs co-exist on separate arrays, just like the Standard SAS
Adapter would do.
Easy Tier: SSDs and HDDs co-exist under the same array.
When under the same array, the adapter can automatically move most accessed data to
faster storage (SSDs) and less accessed data to slower storage (HDDs). This is called Easy
Tier.
There is no need of coding or software intervention once the RAID is properly configured.
Statistics on block accesses are gathered every minute and once the adapter realizes that
some portion of the data is being frequently requested, it will move this data to faster devices.
The data is moved in chunks of 1 MB or 2 MB called “Bands”.
From the operating system point-of-view, there is just a regular Array Disk. From the SAS
controller point-of-view, there are two arrays with parts of the data being serviced by one tier
of disks and parts by another tier of disks.
Figure 2-21 on page 58 shows a diagram of an Easy Tier array.