Seagate 12 TB Exos X12 3.5 Inch Enterprise Class Internal Hard Drive (7200 RPM, 256 MB Cache, SATA 6 Gb/s, Up to 261 MB/s, Model: ST12000NMZ007/NM0007)

Approx 0.33% per year failure rate, 1 in 300 per year, 10x better than some other drives (Backblaze hard drive stats for 2018)Almost 9TB free space with two drives SHR BTRFS in a DS918+ (not on the Synology compatibility list for the DS918+, but does work -- listed compatible with the very similar DS1019+)Can be heard across the room when seeking, but I decided on reliability and speed vs low noise.Also has 10x better URE read error spec than most drives, less than 1 in 10^15 (good if you need to replace a drive. Datasheet with specs available online)5 year warantee when registered (easy online). I leave them running all the time, don't hibernate the drives, or power cycle the NAS every day.

Beware! I bought the 6tb version specifically for the 5 year warranty, however despite the drive being sold and dispatched by Amazon themselves it's an oem drive! I'm unable to register it currently here in the UK. The warranty also started ticking 7 months ago!Am waiting a response from seagate as to honouring the warranty, if that's a no go then it will be going back.Edit 2/1/20 amending the star rating to three stars...... The email to seagate allowed me to then register the drive to my account with the warranty in place. However that did start ticking 6 months ago......... So depending on how old the amazon stock is you may be missing a bit of warranty.

Bought the 8TB version to store audio files. It's fast as you'd expect. If you have it mounted on rubber grommets the seeking sound is hardly audible. Annoyingly the constant spinning whir it makes is much louder than my IronWolf PRO. It also seems to run hotter.

Bought to replace a failed HDD in a old 24” iMac. You’ll need a glazier’s window sucker to pull off the MacBook’s glass screen and a decent set of screwdrivers to remove the LCD. Happily the iMac supports this capacity of drive with no issue.