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Frank Steinmetzger wrote: |
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> Am Tue, Apr 12, 2022 at 06:01:11PM -0500 schrieb Dale: |
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> |
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>>> The advantage of an integrity scheme (like ZFS or comparing with a checksum |
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>>> file) over your rsync approach is that you only need to read all the datas™ |
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>>> from one drive instead of two. Plus: if rsync actually detects a change, it |
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>>> doesn’t know which of the two drives introduced the error. You need to find |
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>>> out yourself after the fact (which probably won’t be hard, but still, it’s |
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>>> one more manual step). |
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>> In this case, if something had changed, I'd have no problem manually |
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>> checking the file to be sure which was good and which was bad. |
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> Consider a big video file, which I know you like to accumulate from youtube |
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> and the likes. How do you find out the broken one? By watching it and trying |
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> to find the one image or audio frame that is garbled? The drive might return |
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> zeros or other garbage (bit flip) instead of actual content without SMART |
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> noticing it (uncorrectable error). |
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> |
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|
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In this case, I'd likely rename one file and keep them both until I can |
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figure out which is good. That said, I'd certainly keep the backup copy |
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because odds are, it is good since the error came well after my last |
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backup. At this point tho, I don't know what file was on that bad spot. |
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|
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|
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>> Given |
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>> the error is recent on my drive, I'd suspect the backups to still be a |
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>> good file. For that reason, I'd suspect the backup file to be good |
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>> therefore not to be overwritten. I was trying to avoid a bad file |
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>> replacing a good file on the backup which then destroys all good files |
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>> and leaves only bad ones. This is why I like that SMART at least let me |
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>> know there is a problem. |
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> I also tend to rely on smart, but it’s not all-knowing and probably not |
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> infallible. |
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> |
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> |
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|
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|
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This is very true. I mentioned elsewhere that things like spindle motor |
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failure or the motor that moves the heads are usually not detectable. |
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Some component failures can be detected but not all or even most from |
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what I've read. Basically, the best you can hope for is SMART seeing a |
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bad spot on the media itself. That it seems it can detect most of the |
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time. |
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|
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TL;DR next two paragraphs. Just a interesting story along this line. I |
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used to work in parts at a fortune 500 office company. We had millions |
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of dollars of just computer stuff in inventory just for computers. That |
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was in early 90's. They also had copiers and their parts, paper etc |
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etc. We used a NCR computer for a computer system for the whole |
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company. At the end of the building was a speed bump so people wouldn't |
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go flying down the one lane road between the building and fence on the |
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property line. One day a large truck almost empty went a little faster |
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than normal over the last speed bump. It shook the building to the |
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point I could feel it about 150 feet away. The computer room was like |
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50 feet away from that side of the building. It seems the hard drive |
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felt it very well. One, maybe more, of the head(s) got under the media |
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and started peeling it off the platter and made a really ugly screeching |
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sound. No routine shutdown, they just pulled the plug. As you can |
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imagine tho, it did no good. Even way back then drives of that speed |
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were spinning fast enough. I suspect even by the time a person could |
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blink it was way past fixing. |
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|
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That of course was way before SMART came along but SMART would never be |
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able to predict such a failure. Even NCR said it was likely a 1 in a |
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million chance that the truck hits just when the head was moving over a |
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weak spot. Several thousand dollars later, and a private plane bringing |
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in a new drive, the drive was replaced. Of course, the idiot in charge |
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had no backups that were of any use. All of them were several weeks |
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old, likely over a month. Luckily he stayed far away from me for at |
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least a month. Otherwise, I'd likely still be in jail, with my hands |
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around the neck of his corpse. :-@ |
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|
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SMART isn't a sure thing but it can help in some cases which is better |
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than nothing at all. |
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|
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Dale |
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|
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:-) :-) |