Written 22 Aug 2026. Specs from the maker pages linked below. Prices from those stores. I haven't used these. Confirm the diskless SKU before you click. Amazon is full of drive bundles.
Two identical disks mirror each other: SHR ≈ RAID 1 on two bays
Two identical disks: SHR ≈ RAID 1. The third disk is where SHR starts to earn the acronym. RAID is not backup.
Two identical disks mirror each other. On a DS224+ you only have two bays, so SHR or RAID 1 is the decision, and with two matched disks they land in the same place: one disk of usable space, one disk of redundancy. On a DS423+ you can keep adding. That is the only reason this page exists.
| Setup | SHR | RAID 1 |
|---|---|---|
| Two identical disks | Mirror. Usable ≈ one disk. | Mirror. Usable ≈ one disk. |
| Third disk | Becomes RAID 5-like and grows. | Does not add a third member as capacity. You can add a mirror; you cannot just expand RAID 1 by sliding in disk three. Synology community: migrate, don't expect a three-disk RAID 1 volume. |
| Mixed sizes | Uses leftover slices. | RAID 5 / 6 waste down to the smallest disk. RAID 1 usable is the smallest mirror member. |
| SHR-2 | Needs four disks. Two-disk fault tolerance. | n/a |
| DS224+ lid | SHR or RAID 1 (also 0 / Basic / JBOD) | Same two-bay set |
| DS423+ lid | SHR, then 5 / 6 / 10 as you grow | RAID 1 stays a mirror |
Use two matched CMR NAS drives. Example pair: WD Red Plus 8 TB WD80EFPX (CMR, 5640 RPM, 180 TB/yr) or IronWolf 8 TB ST8000VN004 (CMR, 7200 RPM, 180 TB/yr). IronWolf 1–6 TB is 5400 RPM: read the SKU. Skip WD Red EFAX (DM-SMR), WD Blue 3.5" EZAZ, BarraCuda 3.5" 4 / 8 TB SMR. SMR in SHR is how people still have a bad rebuild in 2026.
5400 / 5640 RPM is fine for Hyper Backup and Time Machine. It is not a Proxmox LUN. DS224+ SAN Manager: 2 iSCSI targets, 4 LUNs. Put VMs on SSD if you must host them here at all.
Chassis: DS224+ Amazon B0C6927XPX, B&H 1781611-REG. DS423+: B&H 1757288-REG ($499.99 diskless at research fetch), Amazon B0BXMS9GFF was unavailable 22 Aug 2026. Drives: ST8000VN004, WD80EFPX.
Skip
Skip RAID 0 on a first backup box. Skip “RAID is my backup.” Skip expanding RAID 1 by adding a third disk and expecting more terabytes. Skip SMR. Skip mixing a 4 TB leftover with an 8 TB and calling RAID 5 efficient: that is the SHR use case, and even then you should have planned matched disks.
Sources
WunderTech SHR vs RAID calculator. Need to Know IT, SHR explained. Storage Alchemist, Synology RAID types. Synology community on RAID 1 expansion. DS224+ / DS423+ spec PDFs. I haven't migrated a volume in this lab.