My new RB493G has 9.3% Bad Blocks.
I tried netinstall but the percent does not decrease.
What is the acceptable percent for bad block to get the replacement?
Try to do “Format NAND” from the bootloader menu, you will need serial console to enter the menu. It will fix the blocks.
Already tried “format NAND”. But it did not help.
You can send it to seller for repair, if this number increases.
It just increase to 9.4%.
I try Format NAND again. But the result still 9.4%.
It could be a defective NAND chip, so much is not normal. Call the seller for replacement.
It is now 10.2%.
I called the seller for the advanced replacement.
I have two of RB493G.
The other one also has Bad Block start from 4.x to 7.x now
and I can not clear the bad block by format NAND.
Is it the problem with the NAND part or HW/SW bugs.
Both board has the same build date.
some bad blocks are OK, if the number doesn’t increase quickly, there will be no problems, but over 10% is not OK, and you should replace this one for warranty
I believe I have the same problem … brand new RB493G running for 12 days now, bad blocks count steadily increases from 0.0 % to 6.5 % … the router is on a remote location I can not access right now to try and format nand, is there any other way to test this or stop bad blocks from increasing? What happens it gets beyond 10% … will router stop working… It is critical for me it holds for another three days … should I send autosupport.rif to support or just return the router?
JF
Hi,
I’ve noticed the same strange behaviour of the RB493G board and bad blocks. I had version 6.2 of ROS and was testing this system. The percent of bad blocks was developing from 0,3% to 4,6% in few minutes after loading files to the disc. After filling whole nand disc, I deleted the files and was thinking that all bad blocks were marked, and the counter stopped (at 4,6%). But after uploading files again, the counter started increasing too. It is never ending proces until all available blocks will be marked as bad. It can’t work in this way!
I’ve tried to format NAND few times thru serial port and netinstall system, but without luck 
Even called to the seller with request of warranty change of the board…
But, incidentally, I’ve needed to downgrade the system back to version 6.1 and after the operation… number of bad blocks was reset to 0.0% 
and not increasing at this moment (but without guarantee that not will be…). I really don’t think that the problem resides in the hardware - NAND chipset. It might be a problem with system’s mechanism of detecting and marking bad blocks…
Regs, Jarek
I got the same problem, I bought 2 mikrotiks, also RB493G and the first one, went in like 4 months, 3 times over 5% and I needed to re-install. I assume it isn’t meant to do that? I contacted the seller and I have send the routerboard. A few days agter/ago I got a new one, and it’s running for 2.5 days already. The thing is that it already has 0.8% bad blocks :/.
So it can’t be a hardware problem as both routerboards we bought had the same problem.
You had downgraded the system to 6.1, do you mean the routerOS version?
But what I do find strange is that (almost) every time when the system went over 5%, I couldn’t boot because the NAND was corrupted.
mine ran up to 8% nand corruptin (lasted for almost a week) than it crashed… nand format did not help, bad sector count remains. On the first rb493g i was running routeros 5.xx but on replacement unit I tried running routeros 6.4 but the result is the same … bad sector count increases with time … there is something very very wrong with rb493g boards …
JF
It seems the problem isn’t on the hardware but it’s the software.
An update to the major version 6.x (tested on 6.4) will solve the problem.
We know that now for sure, as the problem disappeared when a friend updated to 6.4
Hmm, there is some strange things related to MicroSD card onboard. The percentage of bad blocks was increasing when this card was inserted. When I removed the card and formatted nand - the problem with bad blocks disappeared 
My router works 1 month without restart and numer of bad blocks is still 0.0%
It is very strange behaviour because no data was writting to SD card, only to the internal nand, but still percentage was increasing…
If you are using SD card onboard try to remove it. In my case it solved the problem.
It looks like this is working for me too … will test further.
JF
Worked for me too, removed the SD and no more bad blocks 
Three days of operation including some random stress testing nand (manual read/write file transfer, backup, 5min graphing) produced no bad sectors… it looks like inserted microSD card is the culprit nevertheless it is not being used at all and is on its own defect free. Will keep testing.
JF