Chapter 20. Tuning for Performance

The RAID levels that are most commonly recommended are RAID 6 and RAID 10. RAID 6 provides better space efficiency, good read performance and good performance for sequential writes to large files.

When configured across 12 disks, RAID 6 can provide ~40% more storage space in comparison to RAID 10, which has a 50% reduction in capacity. However, RAID 6 performance for small file writes and random writes tends to be lower than RAID 10. If the workload is strictly small files, then RAID 10 is the optimal configuration.

An important parameter in hardware RAID configuration is the stripe unit size. With thin provisioned disks, the choice of RAID stripe unit size is closely related to the choice of thin-provisioning chunk size.

For RAID 10, a stripe unit size of 256 KiB is recommended.

For RAID 6, the stripe unit size must be chosen such that the full stripe size (stripe unit * number of data disks) is between 1 MiB and 2 MiB, preferably in the lower end of the range. Hardware RAID controllers usually allow stripe unit sizes that are a power of 2. For RAID 6 with 12 disks (10 data disks), the recommended stripe unit size is 128KiB.

In the JBOD configuration, physical disks are not aggregated into RAID devices, but are visible as separate disks to the operating system. This simplifies system configuration by not requiring a hardware RAID controller.

If disks on the system are connected through a hardware RAID controller, refer to the RAID controller documentation on how to create a JBOD configuration; typically, JBOD is realized by exposing raw drives to the operating system using a pass-through mode.

In the JBOD configuration, a single physical disk serves as storage for a Red Hat Gluster Storage brick.

JBOD configurations support up to 36 disks per node with dispersed volumes and three-way replication.