Let me help you with this one.
I first want to thank you for sharing all those details with us but there is some more information I would like to ask you so that I can have a very and more clear image of your issue.
Please answer this:
- Was this working fine before? For how long have you been using this Raid 5?
- What is the NAS brand and model? Are you still running this RAID 5 with that NAS?
It is important to say that the cluster size depends on the file size you will handle. Here is a very good article you can check about it:
NOTE: These links are being offered for your convenience and should not be viewed as an endorsement by Intel of the content, products, or services offered there.
I can also confirm that rebuilding a RAID 5 with that amount of Disks and capacity of each drive will take some time so it may be expected if you find the rebuilding process slow.
I have the same problem on my backupserver. This is my configuracion:
Asrock H87 PRO4
12GB DDR3 1600 (no ECC)
64GB SSD (system) + 5X Caviar Red 4TB RAID5 (Data)
I have another with
asrock H87 PRO4
4GB DDR3 1600 (No ECC)
120GB SSD (system) + 1X 4 TB RED (data)
this is the result: