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Re: Growing SCSI defects list

On Oct 5, 2009, at 2:17 PM, wrote:
One of my scsi disks has a constantly increasing "grown defects list",
i.e. every month or so, the list grows. At the moment:

Primary defects list has 2565 defects
Grown defects list has 174 defects <- this list keeps increasing

Is this normal, or does this mean my disk is failing and needs replacing asap?

A small # of defects, which grows slowly over time is normal. If the # is increasing faster than once a week or so, it's a sign that the drive is on it's way out. smartmontools from pkgsrc can do more precise testing and give you better insight.

Also, how does it detect and manage new defects? What happens to the
data on defective sectors, does it silently get truncated to 0s, or is
there some kind of failsafe way to remap the sectors and keep the data
intact? If so, what is the limit on how many defects can be fixed this
way, before I start losing data?

Every sector has checksums, and in most drives these are actually using Reed-Solomon ECC or variants thereof, which usually allows the drive to recover the data even if some bits are corrupted-- this is SMART ID 195 aka Hardware_ECC_Recovered. Depending on the drive firmware, if it notices a problem, it will attempt to reassign the bad sector to a list of spares which are kept around for this purpose; but some drives will only do this when a sector is written to. You can also use the SCSI "reassign block" command to do this process manually if you know from error logs that a particular sector is being reported as bad.

You'd have to contact your drive's manufacturer to determine how many spare sectors they've allocated with their default formatting, and this is likely a tunable value by adjusting the SCSI mode pages and doing a "format unit". Doing a reformat or a write of all-zeros is a pretty good way of forcing the drive to reallocate all bad sectors (although you'd need to backup and restore your data).

Some random links:,_Analysis,_and_Reporting_Technology


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