RAID and disk layout
Two disks in a mirror is the default for a reason. But a mirror is not a backup, and the difference matters the day something goes wrong.
What RAID is for
One thing only: keeping the machine running when a disk dies. With a mirror, a failed disk is a ticket and a swap, not a restore. Without one it is downtime and whatever your last backup holds.
What it does not protect you from
- A wrong command.
rm -rfis written to both disks at exactly the same speed. - Ransomware or a compromise. Same story.
- A corrupt database. The disk is fine; your data is not.
- A failed reinstall. The array gets wiped as cheerfully as a single disk.
So: mirror for uptime, back up for survival.
Software or hardware
Linux software RAID is predictable, visible and portable between machines, and on modern hardware it costs you nothing measurable. A hardware controller with a cache and a battery makes sense for write-heavy databases. If you have no opinion, ask us for one.
Watch it, or it is decorative
An array that is degraded for six months is a single disk waiting to fail. Check
/proc/mdstat or your controller's tool from a monitoring script, and
make sure the mail it sends actually reaches someone. See
checking disk health.
Tell us what you want before delivery
Layout, array level and partitioning are part of the build. Say what you want in the quote and the machine arrives that way, which saves you a reinstall on day one.
Still stuck? Mail support@novogara.com — an engineer answers, at any hour. Back to the knowledge base