I dont know why.
And I have another question.
If the radz2 onlycaluculate 5 disks,the space is 27.3TB,Iknow some spacewill storage some raid &system information,but is it normal for 1TB?
Sorry for my english is not very good,and I dont know how to upload the screen cut.
Did you have 510TB drives in Raid-Z2 and then used the Raid-Z expansion feature to add a sixth drive to get to the 610TB Raid-Z2 listed in the title?
The reporting on drives is in Tibibytes, TiB (1024) and not Terabytes TB (1000). I think this is what you are also seeing. (abbreviations might not be the same internationally)
If you used Raid-Z expansion, the GUI doesn’t show the increased space correctly. You have to use the command line (CLI) to see it.
You can search the fourums for the RAID-Zx-expansion tag and it should be explained in a few of the posts.
6x 10TB RAIDZ2 will give you 4x 10TB useable space = 40 * 10^12.
This will be reported in TiB where a TiB = 2^40.
40TB = c. 36.4TiB.
As @SmallBarky said, if you started with a 5x 10TB RAIDZ2 you would have 30TB = 27.3 TiB.
And if the pool was empty when you expanded it, due to the bug this would remain the free space displayed even though it was in actuality now 36.4TiB.
You can see the actual space used with zpool list
which is accurate and based on actual blocks including parity rather than useable space excluding parity.