Need help - Upgrading my hard drives

Hey, I wonder if someone could help me out.

My current setup: DS920 with 4 x 4TB raid 5, total usable 12TB (9.5TB used)
I have bought 3 x 12TB, and would like to setup raid 5, and total usable space should be 24TB.

What would be the easiest way to upgrade?

What I have done so far was remove 1 of the 4TB at a time and resync with a 12TB, but when I finished that the pool (12TB x3, 4TB x 1) is still 12TB. How can I permanently remove the last 4TB and leave my 3 x 12TB as raid 5 (24TB usable space)

Thank you in advance!

1 Like


I think that RAID5 is your “problem”. As far as I know, you can only benefit from more space when upgrading to larger hard drives, when using SHR1 (which is similar to RAID5) or SHR2. In normal RAIDs the size of the usable space depends always from the smallest hard drive.
As far a I know, unfortunately you only can migrate from RAID5 to SHR1, if you could add one more drive. In your case, this isn’t possible, because all your drive bays are occupied.
So if you want to use all the space you have to replace the last 4 TB hard drive to another 12 TB hard drive or you have to copy all the data from your NAS, wipe the data, delete the RAID5 and configure a SHR1.


Thank you @OliOS2 !
Looks like I have a couple of options already, either way I will need to backup all my data and rebuild the raid.

I am not familiar with SHR1 or SHR2, I believe this is the best time for me to look into these 2 options, and I appreciate your insightful suggestions!

Thanks again!

Hi Pudding,

your welcome.
SHR1 is similar to RAID5 and SHR2 is similar to RAID6.
The benefit of SHR1 or SHR2 over RAID5 and RAID6 is, that you can combine hard drives with different sizes and with the Synology Hybrid Raid (SHR) in this case your NAS can use more space than with normal RAIDs.
In your case with RAID5 (3x12 TB and 1x 4 TB) you get 12 TB, but with SHR1 you will get 28 TB, see:
Synology RAID Calculator

1 Like

So the only way that you can fully get what you want (3x 12TB drives) is going to be to backup your data and rebuild your pool as SHR1 or RAID5 with 3x drives. The problem is you cannot decrease the number of drives in a RAID, only increase. Then as @OliOS2 said, SHR will let you mix drive capacity, where as RAID will have every drive act as the smallest drive in the pool.

1 Like

Hi @OliOS2 , SH1 is festinating, and I appreciate you took time and explain to me. I agree SH1 is probably my best bet.

Thanks again!

Thank you @Will, I have already started to back up my stuff. I have purchased a Seagate external drive ( STGX5000400). SMR drive has blown me away with its pity performance, after an hour or so. I guess the cache has run out. The write speed on this drive went down to about 12MB per second. I did used Seatool to check the drive overnight to make sure there is no issue. but 10MB to 15MB write performance is a joke. Another reason to stay away from SMR drives :grin:

OOOOffffff thats pretty rough! Normally sequential writes would be better than that!

1 Like