I don't think it's the NAS that detect bad sector. The HDD itself that detect it and inform the OS. The HDD also will do marking on the map table that the sector cannot be used anymore. What's the ID number and attribute from S.M.A.R.T info?

You can try hook the HDD to PC and check for any error or bad sector using program such as CrystalDiskInfo.
Firstly, you need to understand what is DNS and DNS Server. From Cloudflare site:


DNS Server is the one that manage DNS. It will periodically connect with other server to update the ip address for url.

Pi-hole mostly used for DNS server. Do you change your DNS server to use Google's 8.8.8.8 or Cloudflare's 1.1.1.1?
The reason to use other DNS server instead of default ISP is for bypassing blocked site or security purpose.
Now more people are using pi-hole instead because the DNS list also include list of url to block, such as harmful site url or advertising url.
Usually you will install adblock on every computer browser or phone, but if the router is configured to use pi-hole for DNS, all the devices that use the router connection will be filtered by pi-hole.

Jdownloader is usually used for direct download. Some download site limit your ip can only download 1 time then have to wait how many hours/day. JDwonloader if configured, can make your router disconnect from isp and then connect back to get different ip. It also block cookie and change it's id so that the download site can't identified you, unlike internet browser. Jdownloader also can be used to download youtube video/audio/subtitle.

Edit: added the bold

My problem is whenever I run data scrubbing the synology NAS will throw error like "I/O error" on disk 4, after few months it become got bad sector (only 1).

Even after I replaced with new drive from RMA it still encountered same issue when running data scrubbing.

I did again RMA and replaced second replacement drive but the problem become worst - when copying certain file it will stuck and keep throw bad sector found. I'm running extended smart test for the particular drive but but it stuck at 90% (already more than 24h).

The storage pool now is in warning status with drive 4 status in critical.

I really stuck and do not know what to do next.

Bad SATA cable or connector also can cause communication error thus report it as bad sector. It's more usually happen to cable as can easily damage or low build quality cable. Try to clean the connector slot.

1 new drive and then 2 RMA drive, all end with bad sector? Is the HDD for usage in NAS? You could try getting HDD from different brand to eliminate the possibility the RMA HDD is problematic. But I feel most likely communication error due to damage or dirty connector.

First thing you should do is make a backup of your data, if you don't have it. Doing rebuilding put a lot of stress on the remaining HDD and if another HDD died all the data will be gone. This is assuming you are using RAID5 or SHR.

I already vacuum the NAS and its connector, first drive only detected I/O error and bad sector when running data scrubbing, I plugged it to PC and executed extended smart test with Western D Dashboard but didnt found any problem.

For the second RMA drive, it is indeed a defective drive as the western D dashboard showed "poor" status, extended smart test cant be executed due to error code 4.

It is western D drive for NAS, however the drives I got from RMA are not with RED label.

recertified/refurbished drive don't hv red labels if not mistaken

Yes, i saw there is a "recertified" word.

Is it RMA can only can "recertified" drive? Is it only in Malaysia?

I think you should get a new drive that you buy from store (or borrow a drive that you know is good, or maybe just swap the slots - to confirm this is a drive issue or slot issue).

'Recertified' means the drive are most likely RMA'ed drives but went through a short retest at vendor site to map out the bad sectors or to temporarily 'fix' the original errors (sometimes just by resetting the SMART logs) and then sent to another customer who RMA, hopefully this customer won't see the issue or the drive manage to run/survive until after warranty period is over before the error comes out again.

I though after 1 year, I can't directly get a new replacement from the same shop. Hence I go thru Western D RMA, never expect got this kind of recertified drive.
The second replacement drive now with health status = "poor", cant even run quick SMART test.

If that is possible if NAS slot with problem can caused the drive SMART Status in poor?

I though after 1 year, I can't directly get a new replacement from the same shop. Hence I go thru Western D RMA, never expect got this kind of recertified drive.
The second replacement drive now with health status = "poor", cant even run quick SMART test.

If that is possible if NAS slot with problem can caused the drive SMART Status in poor?

recertified/refurbished drive don't hv red labels if not mistaken

I also got RMA 1 WD HDD last time, sticker write as RED but it's not red colour sticker.
After use about 1 year the drive died.

Sorry, I actually meant you go and buy a new drive, not ask for replacement from the shop or use a RMA drive since an array rebuild (but I'm not sure what scrubbing does) usually involve a lot of read and write from the drives in the array and these 'recertified' drives could be just working well enough to pass but might not last long. The intense read/write during array rebuild will stress/cause these 'recertified'/'walking wounded' drives to fail prematurely.

I hope you find out what's causing the failures.

newbie to nas, if i use 3x 4TB with SHR/RAID5, i got 8TB usable space and 4TB redundant, and if one of the drive kaput, i still can recover all 8TB data?

just considering what's the best for my NAS initial setup

newbie to nas, if i use 3x 4TB with SHR/RAID5, i got 8TB usable space and 4TB redundant, and if one of the drive kaput, i still can recover all 8TB data?

just considering what's the best for my NAS initial setup

Yes, can. If 1 more drive fail during rebuild, all the data will be gone.
Also would be better to use BTRFS filesystem with SHR/RAID5, this filesystem when doing reading/writing will calculate checksum to make sure there's no data error.
If during rebuild and there's data error also will caused all data to be gone.

newbie to nas, if i use 3x 4TB with SHR/RAID5, i got 8TB usable space and 4TB redundant, and if one of the drive kaput, i still can recover all 8TB data?

just considering what's the best for my NAS initial setup

Mix different brands of HDD on the setup also helps to have different failure time for each HDD.

Mix different brands of HDD on the setup also helps to have different failure time for each HDD.

I have WD mix with seagate. Samsung mix with WD in another volume.

Now I standby an extra HDD in case it kaput.

The last kaput time, it took me 3 weeks to order the HDD from Amazon to replace. In order not to lose the data, I got to shut it down while wait for the HDD come.

To mix HDD we need SHR/SHR-2 config is it    if using Raid-5/6/10 can we still mix HDD 

SHR/SHR-2 is for mix volume. But have the rule.

Normal raid or SHR with mix HDD no problem.

Just Use SHR/SHR-2.

  I don't have  SHR, only normal RAID-5/6/10   

Normal raid can mix different size HDD    hurmm good news