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Question and Answer

Connor McDonald

Thanks for the question, Mudassar.

Asked: October 21, 2000 - 8:40 am UTC

Last updated: June 16, 2020 - 3:12 am UTC

Version: 8.1.5

Viewed 10K+ times! This question is

You Asked

Oracle 8i has some new packages for detecting and solving issues related to block corruption. My question is how does block corruption happen when operating system most of the time would have bad cluster remapping?

and Tom said...

Well, the OS doesn't typically do that -- the hardware might.

Block corruption comes into play in many cases.

I've seen RAID software go bad and do the wrong thing in some cases -- so block corruption can be software induced.

I've seen SCSI cables go bad and flip bits on the way in or out -- hardware issue but not disk drive related. If it is on the way in -- it is totally random and hard to track down (a re-read of a block might give a different answer)...

I've seen controller hardware go bad and flip bits. One time -- the controller controled 1 out of 5 disks in a raid array. Every 5'th disk would flip bits every now and then. Very hard to track down.

I've seen the OS report back that it wrote the block but the entire block is ZERO'ed out. Who knows what layer (OS, software, hardware, etc) did this sort of stuff.


Block corruption is rare but it does happen. As databases get larger and larger -- the probability of it happening at some point nears 100%.

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