storage

Drives and storage

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.

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 reading and writing 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 is not a substitute for a backup.