Adaptec Zero Maintenance Cache Protection in detail

Caches on RAID controllers accelerate write accesses. Without protection, however, cache content is lost in the event of a power failure. If the cache currently contains file system metadata, there is a risk that the entire contents of the file system will be lost due to the loss of the cache content.

In the past only BBUs were used for cache protection (see RAID Controller and Hard Disk Cache Settings and Battery Backup Unit (BBU/BBM) Maintenance for RAID Controllers. Adaptec offers an alternative solution with Zero Maintenance Cache Protection for Adaptec RAID Controller. In the long run, this solution is cheaper than a conventional RAID controller with the running costs of BBU maintenance.

MegaRAID controllers offer a similar technology with CacheVault.

How it works

With traditional RAID controllers, a BBU (Battery Backup Unit) protects the contents of the cache. The cache content is preserved because the cache modules are powered by the battery during a power outage. If the battery is empty (usually after 72 hours at the latest), the cache content is also lost.

ZMCP does not use a rechargeable battery. The cache content is protected by the following system:

• A double layer capacitor is connected to the RAID controller.
• This capacitor is fully loaded automatically during server startup.
• In the event of a power failure, the RAID controller uses the power of the capacitor to write the entire contents of the cache (512 MB or 1 GB, depending on the model) to a non-volatile flash memory (similar to a USB stick). Since 4 GB flash memory is usually the cheapest of the quantities produced worldwide, these are installed on the controller. But only 512 MB or 1 GB are needed.

Controller with ZMCP

Adaptec offers the following controllers with ZMCP:

Controller	ZMCP cache protection with
Adaptec SmartRAID 3162(-8i und -8i /e) Controller	ASCM-17F (ZMCP module and capacitor onboard) (6th Gen ZMCP)
Adaptec SmartRAID 3100 Controller	ASCM-35F (onboard ZMCP module with external capacitor) (5th Gen ZMCP)
Adaptec Series 8Z RAID Controller 12 Gb	AFM-700 (onboard ZMCP module with external capacitor) (4th Gen ZMCP)
Adaptec Series 8 RAID Controller 12 Gb	AFM-700 (3rd Gen ZMCP)
Adaptec Series 7 RAID Controller 6 Gb	AFM-700 (3rd Gen ZMCP)
Adaptec Series 6 RAID Controller 6 Gb	AFM-600 (2nd Gen ZMCP)
Adaptec Series 5 RAID Controller 3 Gb	ZMCP (Adaptec Series 5Z models)

Advantages

Adaptec ZMCP offers the following benefits:

• maintenance-free (no renewal of the BBU)
• permanent cache protection (BBU batteries hold data for max. 72 hours)
• less waste heat compared to the battery of a BBU
• lower costs over the lifetime of the server (no BBUs to purchase and replace)

Comparison ZMCP - BBU

The following table shows some differences between ZMCP and a BBU:

Property	RAID controller with ZMCP	RAID controller with BBU
Maintenance schedule	not required	BBU battery to be renewed approx. every two years Continuous monitoring of the battery necessary
Maintenance window	not required	The server must be switched off and the enclosure opened so that the battery can be replaced.
max. reaction time in case of power failure to prevent data loss	10 years	72 hours, even less if the battery does not have full capacity anymore
Charging time	Capacitor is fully charged during system startup	depending on battery between 4.5 and 9 hours
Time until cache protection is available	immediately	24 to 36 hours when battery capacity test is performed
Special requirements	none	ideally have a new battery ready
Disposal	Capacitor is not changed	Battery must be disposed of properly during replacement

Further Information

• FAQs zu ZMCP (adaptec.com)
• The ABC of Zero-Maintenance Cache Protection (adaptec.com)
• Whitepaper: Adaptec Zero-Maintenance Cache Protection (adaptec.com)
• tweaktown.com: Adaptec Zero-Maintenance Cache Protection Explained (tweaktown.com)