Tangible benefits from use of ZFS

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Tangible benefits from use of ZFS

Post by grahamperrin » Sat Mar 16, 2013 10:24 am

Spun off from viewtopic.php?p=4255#p4255

There are probably many documented examples for other implementations of ZFS.

Here, it'll be nice to share some ZEVO success stories …
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ZEVO success story: a comparison with HFS Plus

Post by grahamperrin » Sat Mar 16, 2013 11:00 am

Integrity and reliability

Whilst I have suffered significant failures with HFS Plus: ZEVO has kept good my home directory, and other ZFS datasets.

An example. Not long ago, following a kernel panic, my startup volume had a set of relatively minor issues:

Checking file system
Performing live verification.
Checking Journaled HFS Plus volume.
Checking extents overflow file.
Checking catalog file.
Checking multi-linked files.
Checking catalog hierarchy.
Checking extended attributes file.
Incorrect number of extended attributes
(It should be 1437349 instead of 1437350)
Checking volume bitmap.
Volume bitmap needs minor repair for under-allocation
Checking volume information.
Invalid volume free block count
(It should be 3131446 instead of 3131572)


With Recovery OS 10.8.2 (Build 12C60) I unlocked the volume and prepared to repair the HFS Plus file system. The authentication dialogue persisted long after entry of a password. After an unreasonably long wait I quit without force but then (probably with my next attempt to use Disk Utility) Recovery OS suffered a kernel panic. I suspect that this panic coincided with invisible repairs by fsck_hfs, begun automatically – for a dirty file system – before Disk Utility became usable. Then where previously the set of issues was relatively minor, fsck_hfs found an apparently worse set of errors and critically:

  • a third party app on the startup volume, good before the panics, was unusable following the reportedly successful repair by fsck_hfs.

In the circumstances, unable to guess what else might have gone bad, I chose to restore the entire startup volume from a backup. Major restorations in circumstances such as these are possible, but tedious.

Where's the success?

What's above is essentially a failure story. Sorry! In context:

  • it's difficult to ignore such problems with HFS Plus
  • whilst confidence in the HFS Plus file system was lost, I had no issue with the ZFS file system on the same disk – to me that's a success, a tangible benefit.

Off-topic from ZEVO, feedback to Apple

The panic of Recovery OS 12C60 was reported to Apple on 2013-03-07.

Feedback concerning the state of the HFS Plus file system is drafted.
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Another comparison with HFS Plus

Post by grahamperrin » Sat Mar 16, 2013 11:27 am

Under my devices with known imperfections or suspected issues I mention two hard disk drives:

  • a 500 GB LaCie Big Disk Extreme (300794EK), which has been treated carelessly
  • a 1 TB LaCie Big Disk Extreme (300797EK), which has been treated with care.

Some of my records relating to those two drives are confidential but overall:

  • results of fsck_hfs do not indicate a hardware problem
  • scrubbing with zpool (checking with ZEVO) finds errors – that's a success.

Read that alongside recent advice from raattgift:

… ZFS (when used correctly) mainly lets you know you should throw a drive or cable or power supply away and replace it with a new or known-working one …


(I should throw the drives, but I keep them for test purposes.)
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