Film-Tech Forum ARCHIVE: Reallocated sectors

This is topic Reallocated sectors in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Ken Lackner (Member # 1002) on 12-30-2019, 11:06 AM:

One of the server manufacturers will tell you that a hard disk is considered bad and should be replaced if a single reallocated sector is found. My understanding is that the whole point of reallocated sectors is to mark the sector as bad and not ever use it so the disk can continue to function normally. What are your thoughts on the subject? Should a disk be replaced if a single reallocated sector is found? If not, what is the acceptable limit?

MODS: Please move to Digital forum. I didn't realize I posted this in FHF.

Posted by Marcel Birgelen (Member # 6801) on 12-30-2019, 11:47 AM:

Besides SSDs, who mostly hide the "reallocated sector" thing, because the way a modern SSD is being written to is completely different than hard drives due to wear-levelling, you'll have a hard time finding disks without a single reallocated sector after a bit of use.

The thing to monitor isn't so much the amount of reallocated sectors, because it also depends on the size of the drive, the thing to monitor is much more if this number is growing. If it is rapidly growing, you'll want to replace the drive asap.

Posted by Ken Lackner (Member # 1002) on 12-30-2019, 12:55 PM:

So if I notice a handful of reallocated sectors and the number never grows, I'm probably good, yeah?

Posted by Ed Gordon (Member # 10866) on 12-30-2019, 01:28 PM:

Ken, as Marcel said, if reallocated sector count is not rapidly increasing you should be fine.

Another thing to keep in mind is that the reserved area designated for reallocation of bad sectors is defined by the disk manufacturer and does not dynamically increase in capacity. If you have the bad luck to fill the reserved area, you may loose data.

Posted by Steve Guttag (Member # 268) on 12-30-2019, 10:35 PM:

Generally, with HDDs...I'll allow under 10 Reallocated sectors, unless the drive is 5 years old or more...then I'm much more touchy. It is definitely the case that if you see the count growing in any short amount of time (days, weeks or eve a month)...change the drive. Drives are cheap, downtime isn't.

Posted by John Thomas (Member # 6509) on 12-31-2019, 02:16 AM:

I always defer this sort of question to the Google whitepaper on HDD failure trends:

https://research.google/pubs/pub32774/

quote:
After their first reallocation, drives are over 14 times more likely to fail within 60 days than drives without reallocation counts, making the critical threshold for this parameter also one.

Like Steve said: drives are cheap, downtime isn't.

Posted by Steve Guttag (Member # 268) on 12-31-2019, 05:59 AM:

I have not found the odd reallocation to be an indicator of pending failure. On the sites we support, I keep a file that tracks the reallocated sector count to see if there is a trend. Some drives will go years without increasing.

Posted by Mark Gulbrandsen (Member # 72) on 12-31-2019, 08:36 AM:

quote:
I always defer this sort of question to the Google whitepaper on HDD failure trends:

Thanks John! That's one of the best papers on HDD failure I have ever read. And I'm sure Google is more than qualified to write it.

Mark

Posted by Ken Lackner (Member # 1002) on 12-31-2019, 01:41 PM:

Thanks, everyone. I'll definitely keep a close eye on the drive in question here and if the number of reallocated sectors climbs, I'll just replace it.

Posted by Leo Enticknap (Member # 534) on 12-31-2019, 02:59 PM:

While I agree on the rate of rise of reallocated sectors being a significant indicator, that Google paper was written in 2007, and the work it draws on goes back as far as 2000. I would be interested to know if a similar study done now would result in the same conclusions. The mechanics of HDDs must have evolved a lot in the last 12 years, not least because in 2007, the average consumer or server hard drive was around 200 to 500 GB; now, it's around 1 to 4 TB, in the same form factor.

Posted by Mark Gulbrandsen (Member # 72) on 12-31-2019, 03:16 PM:

The date is pretty much irrelevant. We had SMART then and hard drives have not changed that much except for size. And it does not pertain to SSD.

Mark