Greg Freemyer wrote:
I'm also very concerned about silent corruption and we often "verify" our critical large files by performing MD5 verifies against a known good value. Especially when we make copies or move them from one media to another. But in all the cases of silent corruption I've seen, it was never the disk. Instead I've seen it be the cable, the controller, bad memory, bad power supply, but never the disk itself. Not to say the disk controller could not be the cause, just that I have not seen it. I did not read the relevant threads, but do they cover all of these sources of silent corruption, or just if a disk is the source? Thanks Greg
I will second what Greg says, I have debugged a number of corruptions related to filesystems. I have never seen it be the disk, I have seen 3-4 different controllers corrupt (bad PCI/MB interaction-2 different manufacturers controllers, and a bad controller).
And then the #1 issue is actual bad memory or bad power supply in the machine. None of the actual cases I saw actually affected *ONLY* a single disk=they affected all of the disks on the controller, so whatever has to be done would almost have to be done a the filesystem level or the application level. The typical corruption is not data off of the disk, the platters themselves (and the internals of the disk) appear to have very very good corruption detection and correction, it is really really unlikely for a bad sector read to not get caught. The PCI bus only has parity (and likely parity errors on the PCI bus are not being monitored-unless you installed the edac_mc module) so 50% of the errors that happen get missed. This was one of the bad PCI/MB interactions, one of the slots on a certain MB (all of the specific MB with a couple of different companies card) *HAD* to be throttled to not produce corrupt data every 1GB of reads or so.
And internally the controllers often have poor checking, and will miss things if the controller goes bad. The disks themselves appear to have very good internal controls-I have never seen disk electronics screw up and corrupt data either.
Basically don't waste time worrying about the single disk corrupting data silently, worry about everything after the disk first as that is the weakest link of everything and is far far more likely to bite you.
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