SMART - And faulty SATA Cables

[Dave Plaza]

Hi guys, first post here - I specifically joined after trawling the web and unsuccessfully finding a concise explanation - I stumbled upon here and it looks like a lot of clued up peeps

I'm not sure whether or not this is the correct forum but it is a storage related question I guess.

So - I'm interested in how SMART functions.

I understand that SMART is always enabled on the hard drive, that is, it is always internally monitoring itself. If I enable SMART in the motherboard BIOS, then this just means at boot up it will ask the hard drive for it's SMART status. This poll result at boot up doesn't define which attributes are failing like SMART aware monitoring software would - It will just flag up a fail without description.

OK, given that the above is correct - If we split the SMART monitoring parameters into 2 categories - Say, physical monitoring attributes such as "spin retry count", and data monitoring attributes like "CRC errors" -

And this is where my understanding blurs - Could a faulty SATA cable cause a SMART error to flag up at boot up? I understand that the physical attributes of SMART monitoring would not be related to a faulty SATA cable - but surely a faulty SATA cable could cause CRC errors.

And this where it really confuses me - I think CRC errors would flag up with SMART aware monitoring software - But would a CRC error be flagged up by motherboard enabled SMART monitoring at boot up? Would one method miss something that the other doesn't - I guess what I'm trying to get to is, how does a hard drive internally monitor these data attributes, does it not rely on speaking with external software/hardware to check the data side of things?

Hope this makes sense

Dave

 

[Cerb]

The HDD (or SSD) does its own recording of the SMART data, all inside itself, by itself. If it's running as a 8GB-limited drive on an ATA converter, hooked up an ISA disk controller, it will still be recording all that SMART data.

The motherboard, and any software you use to read it, interprets it, and often not well. IoW, it keeps track of them, and it reports them. The drive itself doesn't report whether a particular value is one you should be worried about, or not, at least not meaningfully so (thresholds are typically set to a point where you should have long since replaced it).

UDMA CRC error rate is where a faulty cable would show up. That count won't always be a faulty cable (it could be a disk controller problem, bad OK, bad RAM, or bad PSU, as well), but that's the value that a faulty cable should affect.

 

[corkyg]

I might add, that if a SATA data cable is faulty, you will probably be getting some other error indicators other than SMART. A basic problem with SMART is inconsistency between drive brands.

 

[Dave Plaza]

Hey! Thank's for the speedy replies and the info, I really appreciate it

If it's running as a 8GB-limited drive on an ATA converter, hooked up an ISA disk controller, it will still be recording all that SMART data.

So are you saying that the HDD SMART is monitoring the whole path? If so, wouldn't that mean that there would be some kind of CRC attached to all data for it to do this. I'm a little unsure if CRC is just internal to the disk, meaning it just reads and writes data as part of it's internal process and only checks the internal workings of the drive.

Or is it the case that with SMART enabled on the motherboard it polls the drive at boot up by sending some data with CRC and if there is a data mismatch it flags up as a SMART error?

Thanks again

 

[Cerb]

So are you saying that the HDD SMART is monitoring the whole path? If so, wouldn't that mean that there would be some kind of CRC attached to all data for it to do this.

Yes. Each data transfer to the drive from the controller, and from the drive to the controller, have CRCs to be checked. Now, ages ago, they weren't doing that. Only UDMA and newer modes do CRC checking.

 

[Dave Plaza]

Yes. Each data transfer to the drive from the controller, and from the drive to the controller, have CRCs to be checked. Now, ages ago, they weren't doing that. Only UDMA and newer modes do CRC checking.

You're a star!!! Thank's, I get it now