745N NAS bad block issues

Question

We have deployed hundreds of PV 745N NAS to our customer base and have seen a 100% failure rate in successfully replacing failed drives in them.  We have been sending them back to HQ to get rebuilt.  Various issues will occur, related to bad blocks existing on more than one drive, including: 1. replacement drive is seen by OS or DATA array but not the other, so only one of the arrays rebuilds 2. a second drive fails while replacing the first drive, causing one or both of the arrays to fail (array can sometimes be forced back online in some cases in the controller BIOS)   We have seen these issues with firmware 7208 and 7401 to this point, and the latest firmware 7417 says it fixes (only included related points): 2. Hot plugging a drive in a PowerVault 745 with a clean drive, with automatic failover enabled, does not start the rebuild process. 5. Controller fails to identify a drive with a bad block during a consistency check. 7. Back ground consistency check, when enabled, does not work.   Has anyone else seen this problem, and has the firmware update fixed the problems in not seeing the bad blocks in time?

Storagetalk · Answer

You might want to call Dell support about this one.

saqabola · Answer

I have asked Dell Support many times.  The response is along the lines of upgrade the Firmware, driver and BIOS, but after the fact does not help at all.  Bad blocks are bad blocks.  Does anyone know the difference between consistency check and background consistency check on CERC controllers?

Storagetalk · Answer

The reason I say that is because you may need to get all your drives replaced. Sounds like you have a physical problem with your disks.

consistency check command

The controller continuously performs a verification on a redundant array to data integrity. In the case of RAID 1 or 10, consistency checks assure that the data between like blocks match. In the case of a RAID 5, consistency checks assure that data in the stripe and the calculated parity for the stripe match.

background consistency check

Consistency check performed as a background process. See also consistency check command.

Taken from the CERC User Guide on support.dell.com. They are the same thing.

saqabola · Answer

I understand the consistency checks, what I have found is that background consistency check is disabled by default on all of our 745N NAS.  We have hundreds of these NAS, and I have personally seen at least 20 of them have bad blocks that go undetected, due in most part from what I have seen, a problem with firmware older than build 7417.  Recently we have seen the PE 2850 have performance problems because of a similar consistency check, but this one enabled.  The NAS background consistency check is enabled in the controller utility on boot, not from the OS.

PowerVault

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