Basic Software & Hardware: Storage System Components
Basic Software & Hardware
This domain covers the physical storage system and the software that manages it. Expect questions on controller enclosures, disk enclosures, cache, BBU or supercapacitor, SAS/NL-SAS/SSD media, front-end and back-end ports, and management software such as Huawei DeviceManager. Know what each component does and which failure it protects against.
Core rules
- Controllers run the storage OS and process I/O; dual controllers provide redundancy, but they must be in separate fault domains and have consistent software versions.
- Cache improves performance; a BBU or supercapacitor protects dirty cache data during power loss. Cache is not persistent storage.
- SAS HDDs suit performance-sensitive block workloads; NL-SAS suits capacity; SSDs suit low-latency workloads. Mixing media requires tiering or careful pool design.
- Huawei software features: SmartTier moves data between tiers; SmartQoS limits workload I/O; HyperSnap creates snapshots; HyperReplication copies data remotely; HyperMetro provides active-active local dual-site; SmartMigration moves LUNs.
- UltraPath provides multipathing on hosts, presenting redundant paths to a LUN.
Worked example
A host has two FC HBAs and the array has two controllers. With UltraPath, each LUN is visible through two paths. If one HBA or controller path fails, I/O continues over the remaining path. The reasoning: multipathing is a host-side path-redundancy function, not a replacement for array-side RAID or remote replication.
Traps
Do not confuse snapshots with backups; snapshots share the source and can be lost with it. Do not assume a BBU protects user data after cache is flushed. Do not put both controller paths on one switch without verifying redundancy.