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Quick vs long format

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Rick Law:
Happy New Year!

I am doing my year end backup, so I was doing things the same way I have been doing for years.  Surface scan and formatting new drives to store useful backups.  On suspected drives (this year, I have one that all files reads ok but chkdsk doesn't finish), I off-load and surface scan, reformat and then copy back.  I know that probably was caused by ultra long filenames.  It is a repeatable error with XP era machines.  But I surface test and reformat (long instead of quick format) to be sure.

Dumb mindless work doing backup is.  But this time a thought hit me:  With all that intelligence in the drive firmware, it re-allocates bad sector all by itself...  Doesn't that make long format and surface scan a waste of time?

I sure like to hear your experience/opinion.

The sector reallocation built in to the drive firmware can only work if the drive is asked to read the data in question, so the act of reading data is probably more beneficial than scanning it. Modern filesystems (eg: zfs, btrfs) have a 'scrub' operation, which causes every used sector to be read at least once. If the firmware has to reallocate data, it will do so silently. If it can't, then any redundancy built into the higher level file system is used to re-create the data, and write it back (drive firmware will write it to a different physical sector).

When to use full format:

- You are formatting a (software) RAID volume that must be block synchronized.
- For cold storage. you are making it your future self easier to read data after a disk crash. All non-relevant data will be erased instead of random.

--- Quote ---Doesn't that make long format and surface scan a waste of time?
--- End quote ---
Most of the time, yes. if you need it because your drive threw an error, the disk is EOL.

Best insight into disk health:

David Hess:
Doing a surface scan of the drive by *writing* to every sector will force reallocation on write for bad sectors.  Reading the drive will leave bad sectors in place and increase the pending reallocation counter. (1)

So my preference now is to write to the entire drive to force reallocation and then check the SMART parameters.  This year I found three drives which were in the process of failing.

(1) This means that if you have a degraded RAID which keeps dropping a drive and becoming unavailable because of bad sectors, rewriting the bad drive can restore proper operation with bad sector data in only the damaged files unless metadata is affected.  I recovered a 4 x 3TB drive RAID5 last year using this method.  The lesson learned was *always* do a sector scan before swapping a RAID drive.

You can also ask the drive firmware to do a surface scan in the background.
Extended Self Test

I have programmed my server to this once every few months. It takes hours though.


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