How do you have an 18 drive RAID 5? More importantly, why would you put your data at risk like that? RAID 0 is also not a good idea for data you care about.
Looks like it is actually a RAID 6 (z2) striped across 3 volumes (RAID 60). Set it up a while ago (my old one was a 5).
I run crashplan on it as well. A NAS is not a backup.
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[wpiman@nas ~]$ zpool status
pool: tank
state: ONLINE
scan: scrub repaired 0B in 2h27m with 0 errors on Mon Apr 1 04:27:44 2019
config:
NAME STATE READ WRITE CKSUM
tank ONLINE 0 0 0
raidz2-0 ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_23D3JZUAS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_461ZGR8GS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_23DER83GS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_4620K40GS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_83O2GRAKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_46209S9GS ONLINE 0 0 0
raidz2-1 ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_83O2GRYKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_46209RZGS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_83O2GSLKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_85DATG5GS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_83O2GTBKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_4620JUNGS ONLINE 0 0 0
raidz2-2 ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_83O2JLNKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_85EB6W3GS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_93H57EJKS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_461Z9GRGS ONLINE 0 0 0
ata-TOSHIBA_DT01ACA300_Y44TZPWGS ONLINE 0 0 0
ata-TOSHIBA_HDWD130_85EB6W7GS ONLINE 0 0 0
logs
mirror-3 ONLINE 0 0 0
ata-INTEL_SSDSC2BA100G3_BTTV4222016H100FGN-part1 ONLINE 0 0 0
ata-INTEL_SSDSC2BA100G3_BTTV422203UF100FGN-part1 ONLINE 0 0 0
errors: No known data errors