Weird read and write behaviour [SOLVED, DUMBASS QUESTION]

[hema]

My Unraid started to behave oddly. It seems to read and write equal amount to all active disks even if it should only be writing to them.

 

I have been trying to build the array on several different configurations, 2 and 1 parity disk, 4 to 12 disks and every time I get the same weird (and slow) performance. Disks used in tests were 2, 3 and 4TB SATA.

I used to have properly working array with the very same Unraid-USB stick earlier but with SAS disks.

 

It also seems to first buffer the data into memory and dump it to disk later.  

 

Attached captures illustrate what I mean. There is no traffic on the array disks but the NFS copy over the 10Gb network. 

 

Any ideas on what might be wrong?

  

Edited October 17, 2019 by hema

[Squid]

29 minutes ago, hema said:

also seems to first buffer the data into memory and dump it to disk later.  

As it should.

29 minutes ago, hema said:

Unraid started to behave oddly. It seems to read and write equal amount to all active disks even if it should only be writing to them

Because with the parity system it has to know the previous contents and the new contents so that the parity drive will remain in sync

[Squid]

You can however speed up writes by enabling reconstruct write in disk settings, at the expense of all drives must be spinning 

[hema]

OK, now I see.

 

The previous array was of SAS disks which do not spin down and therefore I had not seen this mode of operation before.

 

Thank you for explaining.