Chapter 9. Configuring Red Hat Storage for Enhancing Performance

This chapter provides information on configuring Red Hat Storage and explains clear and simple activities that can improve system performance. A script that encodes the best-practice recommendations in this section is located at /usr/lib/glusterfs/.unsupported/rhs-system-init.sh. You can refer the same for more information.

9.1. Disk Configuration

Prior to Red Hat Storage 3.0.4 release, storage for Red Hat Storage bricks was configured on hardware RAID devices created from multiple physical disks. Red Hat Storage 3.0.4 adds support for JBOD (Just a Bunch of Disks). In the JBOD configuration, a single physical disk serves as storage for an Red Hat Storage brick. JBOD is supported with three-way replication. Red Hat Storage in JBOD configuration is recommended for highly multi-threaded workloads with sequential reads to large files. For such workloads, JBOD results in more efficient use of disk bandwidth by reducing disk head movement from concurrent accesses. For other workloads, two-way replication with hardware RAID is recommended in the Red Hat Storage 3.0.4 release.

9.1.1. Hardware RAID

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.
For 12 disks, RAID 6 volume can provide ~40% more storage space as compared to RAID 10 volume, which will have 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 provisioning, the choice of RAID stripe unit size is tied closely with the choice of thin-provisioning chunk size.
For RAID 10, a stripe unit size of 256KiB 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 1MiB and 2MiB, 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.

9.1.2. JBOD

Important

  • The number of disks supported per server in the JBOD configuration is limited to 24.
  • JBOD is supported with three-way replication.
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.