storage
Drives and storage
Array at a glance
RAID 10 from four 1TB drives — principle and capacity
RAID10 (sometimes written RAID 1+0) combines striping and mirroring: data is first duplicated into pairs (mirror), and those mirrored pairs are then striped for higher performance. RAID10 needs at least 4 drives. I also keep a fifth drive attached to the array as a spare — if a drive in the array fails, the spare automatically replaces it and the array rebuilds the failed drive's data onto it. I get an email notification whenever any drive in the RAID array fails.
Why use bcache (SSD as cache)
The bcache service lets you use a fast SSD as a cache in front of slower block devices (HDDs, or even an MD/RAID array). The benefit is a significant speed-up for writing and reading frequently accessed data, without needing to move all your data onto SSD. On my 2TB storage pool I run a 250 GB SSD cache.
Monitoring and maintenance
- One of the other OpenMediaVault services I rely on is SMART status monitoring for both HDDs and SSDs — the system emails me if something goes wrong, whether at the SMART level or the RAID level.
- Important, critical data is also backed up elsewhere, off the NAS — RAID should never be considered a form of backup!