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Homelab · Guide · By Mohammed Almuhanna · Updated
Which RAID should I use?
Most RAID advice hides behind "it depends." It mostly does not. Your drive count, drive sizes, and what runs the box decide this for you, and the five questions below get you a straight answer, including what you give up. I run SHR-1 on my own Synology and I will tell you exactly when I would not.
The three questions that actually decide it
Do you have a real backup? This one outranks everything. RAID keeps the array online when a drive dies; it does not protect you from a deleted folder, ransomware, or the whole box dying. If you have an offsite copy, single parity is a reasonable trade and you keep more space. If the array IS the only copy, no RAID level fixes that, and you should spend the money on a backup before a second parity drive.
How big are the drives? Rebuilding a dead drive means reading every surviving drive in full. On 4 TB drives that is hours; on 12 TB drives it is the better part of a day, and the whole time a single-parity array is one read error away from losing everything. That is why my answer flips from single to double parity around the 8 TB mark. The rebuild-risk numbers make the case with real math.
What runs the box? A Synology wants SHR. TrueNAS wants RAIDZ. unRAID is its own model and the reason to pick it in the first place is mixed drives. Fighting the platform's native layout buys you nothing; I picked SHR-1 on my DS1522+ because it is the layout the box is built around, not because SHR beats ZFS in some abstract sense.
What I run, so you can weigh my bias
Five matched 12 TB IronWolf Pro drives on SHR-1, which is single parity, on a Synology. By my own 8 TB rule that deserves an eyebrow. The reason I sleep fine is the first question above: there is a real offsite backup behind the array, so a failed rebuild costs me a restore, not my data. If that backup did not exist, I would be on SHR-2 and short one drive of space.
Common questions
Is RAID 5 dead?
No, but its safe zone shrank. On small drives with a backup behind it, single parity is still a fine trade. On 12 TB drives holding your only copy, it is a gamble. The level did not change; the drives got big enough to make its rebuild window dangerous.
Should I use RAID 6 or RAID 10?
RAID 6 for capacity and surviving any two failures; RAID 10 for speed and fast rebuilds. If the box serves files to a handful of people, RAID 6. If it hosts VMs or databases that hammer disks, RAID 10 earns its missing capacity.
Is SHR better than RAIDZ?
Wrong question; they live on different boxes. SHR is the right call on a Synology (mixed sizes, one-drive-at-a-time growth), RAIDZ is the right call on TrueNAS (checksums, scrubs, snapshots). Pick the platform first and the layout mostly picks itself.
How many drives can fail before I lose data?
Single parity (RAID 5, RAIDZ1, SHR-1, unRAID single): one. Double parity (RAID 6, RAIDZ2, SHR-2, unRAID dual): two. Mirrors: one per pair, more only if you mirror deeper. unRAID is the graceful loser here, because a failure past parity loses only the files on the dead disks, not the whole array.