HPE Smart Array P824i-p MR Gen10 User Manual page 27

This controller now supports two power options to enable the controller cache features. Collectively, these
two options are known as the "energy pack" and include the following:
• HPE Smart Storage Battery
• HPE Smart Storage Hybrid Capacitor
For more information about these options, see "Energy pack options."
NOTE: Write back caching is enabled when the energy pack is installed and charged. Write Through is
enabled when the energy pack is not installed, if the charge is low, or if it fails during a relearn cycle. To
monitor the status of the energy pack, use iLO.
Since the interface does not display the cache policy used during the creation of the logical drive, you can
identify the policy by:
• viewing the energy pack charge status in iLO and the write cache status
• view cache policy information in the event log
• temporarily disabling the cache, which displays the original cache setting
I/O policy
The I/O policy applies to reads on a specific logical drive. It does not affect the read ahead cache. The I/O
options for the logical drive are:
• Direct IO - In direct I/O mode, reads are not buffered in cache memory. Data is transferred to the
cache and the host concurrently. If the same data block is read again, it comes from cache memory.
This option is the default setting.
• Cached IO - In cached IO mode, all reads are buffered in cache memory. This option is suited for once
write and multiple read workloads.
Drive caching
The drive caching options for the logical drive are:
• Unchanged - Leave the current drive cache policy as is.
• Enabled - Enable the drive cache
• Disabled -- Disabled the drive cache
Stripe size selection
When a logical drive is created, the unit of data that it manipulates is defined as a "strip" (ranging in size
from 64 KiB to 1 MiB). These strips are distributed across the physical drives in the array. A "stripe" is one
set of strips. Striping helps to distribute the I/O workload across multiple physical drives. HPE Smart Array
controllers configure strips, not stripes.
You can calculate the stripe size from:
• Strip size
• Number of physical drives in the logical drive
• RAID level
Features 27