Template:CephHardwareRAID

Hardware RAID Configuration

Ceph has the ability to repair itself in the event of the loss of one or more OSDs which can be provisioned one-to-one with each Storage Pool which is one-to-one with a HDD. In QuantaStor deployments we support this style of deployment but our reference configurations always use hardware RAID to combine disks in to 5x disk RAID5 groups for several reasons:

• Disk failures have no impact on network load since they're repaired using a hot-spare device associated with the RAID controller
• Journals can be made fault-tolerant and easily maintained by configuring them into RAID1 or RAID5 units.
• Multiple DC grade SSDs can be combined to make ultra high-performance and high-endurance Journal Devices and the sequential nature of the journal writes lend well to the write patterns for RAID5.
• Disk drives are easy to replace with no knowledge of Ceph required. Simply remove the bad drive identified by the RED LED and replace it with a good drive. The RAID controller will absorb the new drive and automatically start repairing the degraded array.
• When the storage is fault-tolerant one need only maintain two (2) copies of the data (instead of 3x) so the storage efficiency is 40% usable vs. the standard Ceph mode of operation which is only 33% usable. That's a 20% increase in usable capacity.
• RAID controllers bring with them 1GB of NVRAM write-back cache which greatly boosts the performance of OSDs and Journal devices. (Be sure that the card has the CacheVault/MaxCache supercapacitor which is required to protect the write cache).
• Reduces the OSD and placement group count by 5x or more which allows the cluster to scale that much bigger and with reduced complexity (a cluster with 100,000 PGs use less RAM per appliance and is easier for Ceph monitors to manage than 500,000 PGs).

Besides the nominal extra cost associated with a SATA/SAS RAID Controller vs a SATA/SAS HBA we see few benefits and many drawbacks to using HBAs with Ceph. Some in the Ceph community prefer to let bad OSD devices fail in-place never to be replaced as a maintenance strategy. Our preference is to replace bad HDDs to maintain 100% of the designed capacity for the life of the cluster. Hardware RAID makes that especially easy and QuantaStor has integrated management for all major RAID controller models (and HBAs) via the Web UI (and CLI/REST). QuantaStor's web UI also has an enclosure management view so that it's easy to identify which drive is bad and where it is located in the server chassis.