IBM FlashSystem 840 Product Guide
10
Table 5 lists the supported flash modules.
Table 5. Supported flash modules
Description
Feature code
Maximum quantity supported
1 TB eMLC Flash Module
AF1B
12
2 TB eMLC Flash Module
AF10
12
4 TB eMLC Flash Module
AF11
12
For RAID 0, these configurations have capacity points of 2 TB, 4 TB, 6 TB, 8 TB, 10 TB, 12 TB, 16 TB, 20
TB, 24 TB, 32 TB, 40 TB, and 48 TB.
For RAID 5, these configurations have capacity points of 2 TB, 4 TB, 6 TB, 8 TB, 10 TB, 12 TB, 16 TB, 20
TB, 24 TB, 32 TB, and 40 TB.
IBM Variable Stripe RAID
Variable Stripe RAID data protection is a unique, self-healing data protection that is managed
independently by each flash controller on each flash module. With Variable Stripe RAID, every flash
controller creates a striped data layout across its set of 10 chips similar to a 9+1 RAID 5 array with
rotating parity. The Variable Stripe RAID stripe (page) size is 4 KB. When the Variable Stripe RAID
algorithm detects a failure affecting one or more flash module in a RAID stripe, the following process
happens:
Data that is stored in the affected regions is reconstructed from the remaining data/parity elements in
1.
the stripe.
All pages in the affected stripe, including the reconstructed data, are moved to reserved space
2.
(overprovisioned area).
Subsequent requests for data in the affected stripe are directed to the new locations (now part of the
3.
normal storage area in the system).
The original location of the affected stripe is added to the available overprovisioned area as a (n-1) +
4.
parity stripe. (For example, if the affected stripe was a 9+1 stripe, it becomes an 8+1 stripe.).
No system-level rebuild process is necessary to maintain data protection or usable capacity after a failure
caught by Variable Stripe RAID. Further more, the entire Variable Stripe RAID recovery process is
automatic and transparent to the user and administrator, and typically takes place in less than a second.
Variable Stripe RAID activities are not normally tracked in system logs, but the root causes of failures that
are typically handled by Variable Stripe RAID-plane failures and block failures are tracked in system
counters and reflected in the overall flash module and system health metrics.
IBM Two-dimensional (2D) Flash RAID
The combination of IBM Variable Stripe RAID and system-level RAID 5 protection across flash modules is
called two-dimensional (2D) Flash RAID. Variable Stripe RAID automatically and transparently protects
against partial or full flash chip failures within the flash module, with no downtime or maintenance
required. System-level RAID 5 adds protection against complete flash module failure and enables
hot-swappable flash modules. Additionally, all active components are redundant and hot-swappable with
tool-less access from the front or back of the system, enhancing two-dimensional RAID protection.
