Dell PowerVault ME5 Series Storage System CLI Reference Guide

Shows cache settings and status for the system and optionally for a volume.

[<volume>]

<volume>

System cache parameters:

Shows the system’s operating mode, also called the cache redundancy mode:

• Active-Active ULP: Both controllers are active using ULP (Unified LUN Presentation). Data for volumes configured to use write-back cache is automatically mirrored between the two controllers to provide fault tolerance.
• Single Controller: The enclosure contains a single controller.
• Failed Over: Operation has failed over to one controller because its partner is not operational. The system has lost redundancy.
• Down: Both controllers are not operational.

Shows the system's cache block size.

Controller cache parameters:

Shows the current, system-wide cache policy as determined by auto-write-through logic. This value is not settable by users. If an auto-write-through trigger condition (such as a fan failure) is met, the cache policy for all volumes changes to write-through, overriding the volume-specific settings. When the problem is corrected, the cache policy reverts to the value configured for each individual volume.

• Enabled: Write-back. This is the normal state.
• Disabled: Write-through.
• Not up: The controller is not up.

• Enabled: If the controller loses power, it will automatically write cache data to the memory card. Cache flush is normally enabled, but is temporarily disabled during controller shut down.
• Disabled: Cache flush is disabled.

Volume cache parameters:

If a volume is specified, its serial number.

If a volume is specified, its name.

If a volume is specified, its cache write policy:

• write-back: Write-back caching does not wait for data to be completely written to disk before signaling the host that the write is complete. This is the preferred setting for a fault-tolerant environment because it improves the performance of write operations and throughput.
• write-through: Write-through caching significantly impacts performance by waiting for data to be completely written to disk before signaling the host that the write is complete. Use this setting only when operating in an environment with low or no fault tolerance.

If a volume is specified, its cache optimization mode:

• standard: This controller cache mode of operation is optimized for sequential and random I/O and is the optimization of choice for most workloads. In this mode, the cache is kept coherent with the partner controller. This mode gives you high performance and high redundancy.
• standard-atomic-write: This controller cache mode includes the standard mode features but also guarantees that if a failure (such as I/O being aborted or a controller failure) interrupts a data transfer between a host and the storage system, the controller cache contains either all the old data or all the new data, not a mix of old and new data. This option has a slight performance cost because it maintains a secondary copy of data in cache so that if a data transfer is not completed, the old cache data can be restored.
• cache-hit-atomic-write: This controller cache mode includes the cache-hitmode features but also guarantees that if a failure (such as I/O being aborted or a controller failure) interrupts a data transfer between a host and the storage system, the controller cache contains either all the old data or all the new data, not a mix of old and new data. This option has a slight performance cost because it maintains a secondary copy of data in cache so that if a data transfer is not completed, the old cache data can be restored.

If a volume is specified, its read-ahead cache setting:

• Disabled: Read-ahead is disabled.
• Adaptive: Adaptive read-ahead is enabled, which allows the controller to dynamically calculate the optimum read-ahead size for the current workload.
• Stripe: Read-ahead is set to one stripe. The controllers treat NRAID and RAID-1 disk groups internally as if they have a stripe size of 512 KB, even though they are not striped.
• 512 KB, 1 MB, 2 MB, 4 MB, 8 MB, 16 MB, or 32 MB: Size selected by a user.

# show cache-parameters V1

cache-settings

cache-parameter (if a volume is specified)

status

set volume-cache-parameters

show volumes