Western Digital Ultrastar DC HC550 18TB
Enterprise HDD
Part number WUH721818AL5200 · Ultrastar DC HC550 series · NL-SAS 12Gb/s. If your machine is listed below, this drive is officially supported — not a forum workaround.
Part of the Western Digital Ultrastar DC HC550 series →
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Specifications are the manufacturer's published ratings for this product series; verify the exact part number before purchase.
Rated CMR (conventional magnetic recording) — the right recording type for a large cold copy. CMR keeps a full-library backup pass fast even at 16–24 TB, which is the whole point of the offline slot in a 3-2-1 plan: rotate two drives monthly, keep one powered off, and the backup tooling (Veeam, Duplicati, Hyper Backup, HBS 3) does the scheduling. Full rule and vendor tool table: 3-2-1 for NAS.
Compatibility verdict
It appears on the official compatibility lists of 7 machines and series — 7 QNAP. This is a Enterprise-class drive: rated for heavier sustained workloads than desktop drives. It is a strong pick for a NAS running 24/7, large-array rebuilds or camera workloads, and enterprise lines are also the drives most widely listed across all five vendors' HCLs. Its series rating is on file as CMR (conventional) — what RAID rebuilds and full-library copies want.
Compatible NAS models
Same-capacity alternatives
Other drives listed at 18 TB capacity, ranked by how many machines list them:
Quick answers
Is the WUH721818AL5200 officially compatible with my NAS?
It appears on the official compatibility lists of 7 machines and series — 7 QNAP. Every machine page linked below shows the vendor's own list entry, refreshed daily.
Is the WUH721818AL5200 CMR or SMR?
As a Western Digital Ultrastar DC HC550 drive, it is rated CMR. CMR (conventional magnetic recording) is what a RAID array wants: SMR drives slow rebuilds dramatically. See the <a href="/faq/cmr-vs-smr-nas-drives/">CMR vs SMR guide</a> for the full series table.
Is the WUH721818AL5200 a good NAS drive?
This is a Enterprise-class drive: rated for heavier sustained workloads than desktop drives. It is a strong pick for a NAS running 24/7, large-array rebuilds or camera workloads, and enterprise lines are also the drives most widely listed across all five vendors' HCLs. Its series rating is on file as CMR (conventional) — what RAID rebuilds and full-library copies want.
Can I use the WUH721818AL5200 for a 3-2-1 cold backup copy?
Rated CMR (conventional magnetic recording) — the right recording type for a large cold copy. CMR keeps a full-library backup pass fast even at 16–24 TB, which is the whole point of the offline slot in a 3-2-1 plan: rotate two drives monthly, keep one powered off, and the backup tooling (Veeam, Duplicati, Hyper Backup, HBS 3) does the scheduling. Full rule and vendor tool table: 3-2-1 for NAS.
What are alternatives to the WUH721818AL5200?
At the same capacity, the most widely listed alternatives are Seagate ST18000NM000J (211 machines), Seagate ST18000NE000-2YY101 (194 machines), Seagate ST18000NT001-3LU101 (192 machines). The full ranked list is below.