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 RAID controller configuration

OpenStack Object Storage does not require RAID. In fact, most RAID configurations cause significant performance degradation. The main reason for using a RAID controller is the battery-backed cache. It is very important for data integrity reasons that when the operating system confirms a write has been committed that the write has actually been committed to a persistent location. Most disks lie about hardware commits by default, instead writing to a faster write cache for performance reasons. In most cases, that write cache exists only in non-persistent memory. In the case of a loss of power, this data may never actually get committed to disk, resulting in discrepancies that the underlying file system must handle.

OpenStack Object Storage works best on the XFS file system, and this document assumes that the hardware being used is configured appropriately to be mounted with the nobarriers option. For more information, refer to the XFS FAQ:

To get the most out of your hardware, it is essential that every disk used in OpenStack Object Storage is configured as a standalone, individual RAID 0 disk; in the case of 6 disks, you would have six RAID 0s or one JBOD. Some RAID controllers do not support JBOD or do not support battery backed cache with JBOD. To ensure the integrity of your data, you must ensure that the individual drive caches are disabled and the battery backed cache in your RAID card is configured and used. Failure to configure the controller properly in this case puts data at risk in the case of sudden loss of power.

You can also use hybrid drives or similar options for battery backed up cache configurations without a RAID controller.

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