User talk:RobJ

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Rob's unRAID Start Page

I tried to add all I could remember above, some things are still missing, wish I had access to content of original User:RobJ page (bash manual link, temp smart links, other?)

  • Need to add comprehensive Table of Contents wiki page, like a site map. Perhaps start with merger of 'Getting Started' and 'Unofficial Documentation'. Add all wiki pages that are still useful. Then add sections for all FAQ's, guides, and videos.


Reference links


  • Bad block HOWTO - instructions for both zeroing a bad block and forcing a remap, and determining what file contains the bad sector
  • FAQ entry about USB - deals with accessing SMART info from some USB drives. Brian may want to try the '[b]-d usbcypress[/b]' option on the flash drive, and see if there is any SMART info for it (requires smartctl v5.37 or higher)
  • Can we believe S.M.A.R.T. ?
  • This smartmontools FAQ question, and the following one too, deal with uncorrectable sectors on a drive, and remapping sectors - rather interesting.

My ATA drive is failing its self-tests, but its SMART health status is 'PASS'. What's going on?

If your ATA drive supports self-tests, you should run them on a regular basis, for example one per week:

smartctl -t long /dev/hd?

After the test has completed, you should examine the results with:

smartctl -l selftest /dev/hd?

If the drive fails a self-test, but still has 'PASS' SMART health status, this usually means that there is a corrupted (uncorrectable=UNC) sector on the disk. This means that the ECC data stored at that sector is not consistent with the user data stored at that sector, and an attempt to read the sector fails with a UNC error. This can be a one-time transient effect: a sudden power failure while the disk was writing to the sector corrupted the ECC code or data, but the sector could correctly store new data. Or it can be a permanent effect: the magnetic media has been damaged by a bit of dust, and the sector could not correctly store new data.

If the disk can read the sector of data a single time, and the damage is permanent, not transient, then the disk firmware will mark the sector as 'bad' and allocate a spare sector to replace it. But if the disk can't read the sector even once, then it won't reallocate the sector, in hopes of being able, at some time in the future, to read the data from it. A write to an unreadable (corrupted) sector will fix the problem. If the damage is transient, then new consistent data will be written to the sector. If the damage is permanent, then the write will force sector reallocation. Please see Bad block HOWTO for instructions about how to force this sector to reallocate (Linux only).

The disk still has passing health status because the firmware has not found other signs of trouble, such as a failing servo.

Such disks can often be repaired by using the disk manufacturer's 'disk evaluation and repair' utility. Beware: this may force reallocation of the lost sector and thus corrupt or destroy any file system on the disk. See Bad block HOWTO for generic Linux instructions.

smartd is warning that my ATA disk has unreadable or uncorrectable or pending sectors. What's going on?

Disk drives store data in blocks (sectors) of 512 bytes. Each 512 bytes has additional bytes appended to it (usually 40 to 60) which are used internally by the disk firmware for error checking/detection and correction. These are called ECC bytes.

Sometimes the data in a sector gets corrupted. This can happen because a speck of dust scratched the disk, or because the disk was powered down while writing data to that sector, or for other reasons. Usually the ECC bytes can be used to correct the corrupted data. However if the ECC bytes are inconsistent or can't be used to correct the bad data, then the 512 bytes of data are lost. Such a sector is called unreadable or uncorrectable.

If your disk has an unreadable sector, this means that some of your data can't be retrieved. You can force the disk to replace the unreadable sector with a spare good sector, but only at the price of losing the 512 bytes of data forever.

Disks with uncorrectable sectors can often be repaired by using the disk manufacturer's 'disk evaluation and repair' utility (see previous FAQ entry). Beware: this may force reallocation of the lost sector and thus corrupt or destroy any file system on the disk. See Bad block HOWTO for generic Linux instructions.

Normally when an uncorrectable sector is found, the disk puts this onto a 'pending sector list' to indicate that it should be replaced with a spare good sector. However this replacement won't take place until either the disk can read the data on the bad sector, or is commanded to write new data to that bad sector.


Temp holding area

Special Index - moved to UnRAID Topical Index

Rob's Alternative unRAID Wiki start page

unRAID Server is a Network Attached Storage server operating system that boots from a USB Flash device and specifically designed for digital media storage.

For a more detailed introduction see the Overview page.

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Should be considered accurate and up to date (except during periods of beta releases)
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Should be your first port of call when learning to install and operate unRAID

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