About performance hierarchy level 1
Level 1 is the storage portion of a typical disk array. It can be populated with various size of Hard Disk Drives (HDD), typically 7200RPM SAS (Serial Attach SCSI (Small Computer System Interface)) that are dual ported to provide high availability. The storage can also be configured with Solid State Drives (SSD) for environments where access time is critical, such as concurrent read/write operations. As an example, backups with immediate replication to a remote site would benefit from SSDs. HDDs and SSDs are available in SAS configurations as SAS provides a redundant, reliable, mature protocol.
SAS runs at a speed of 12Gb/s in this example. The connectivity from the RAID controllers as well as the controllers themselves are noted with the purple lines and outlines. The connectivity from the controllers to the drives are 12Gb and the drives have a dual ported connection. Each of the drive SAS ports are connected via a SAS fabric with "expander" that allows for a high number of concurrent connections to disks, SSDs, tapes, and RAID controllers. The dual port connection allows for dual controller operation, the whole of which produces a highly reliable solution with 99.999% (5 nines) of availability. This solution is used primarily on the higher capacity systems that require speed and availability as key requirements.
When using disk drives of 1TB or higher capacity, it is highly recommended that users build their systems with RAID 6/dual parity or RAID 10 to ensure that no data is lost due to disk failures. Systems with the size of drives equal to or greater than 1TB take a relatively long time to rebuild to a hot spare that should be included in every system. The long rebuild time creates a need to plan against a second drive failure during rebuild. RAID 6 addresses this as its configuration provides two parity drives.
When creating storage, note that NetBackup supports volumes of up to 32 TiB and a maximum of 6 volumes per NetBackup Media server, so decide on your storage solution with this in mind. As an example, if 4TB drives were used and the volume had 11 drives configured in a RAID6 Logical Unit Number (LUN) the effective capacity in TB would be 4 * (11-2) = 36TB. In TebiBytes (TiB) it converts to 32.74 TiB.
This same type of solution can be created with SSDs. A major consideration is that the speed of rebuild for a disk drive is much longer than an SSD. Rebuilds with a 7.68TB SSD are approximately, 2.25 hours as compared to the 4TB disk drive noted earlier which, if there are numerous volumes being managed by dual controllers, can stretch to 40+ hours. Because of this difference in rebuild speed, with SSD drives, it is possible to build RAID5 volumes and have a fast enough rebuild to remove the need for dual parity. Use cases for SSD include re-hydration of deduplicated data to save to tape and operations, such as multiple concurrent backups and replications.