I ran the "Verify Disk" tool in disk utility on my main disk called Macintosh HD, and it came up with this log:

Verifying volume “Macintosh HD”
Checking storage systemChecking volume.
disk0s2: Scan for Volume Headers
disk0s2: Scan for Disk Labels
Logical Volume Group 4D3DFAA4-7124-4F3F-A19D-D06A1784AB17 spans 1 device
Logical Volume Group has a 16 MB Metadata Volume with double redundancy
Start scanning metadata for a valid checkpoint
Load and verify Segment Headers
Load and verify Checkpoint Payload
Load and verify Transaction Segment
Load and verify Transaction Segment
Incorporate 1 newer non-checkpoint transactions
Load and verify Virtual Address Table
Load and verify Segment Usage Table
Load and verify Metadata Superblock
Load and verify Logical Volumes B-Trees
Logical Volume Group contains 1 Logical Volumes
Load and verify E7324686-925A-48BF-8150-A982F1572F20
Load and verify 82E44F05-FEF5-49A9-B3C6-1911EE30BB49
Load and verify Freespace Summary
Load and verify Block Accounting
Load and verify Segment Cleaning
Newest transaction commit checkpoint is valid
The volume 4D3DFAA4-7124-4F3F-A19D-D06A1784AB17 appears to be OK.
Checking file systemPerforming 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.
Checking volume bitmap.
**Volume bitmap needs minor repair for orphaned blocks**
Checking volume information.
**Invalid volume free block count**
(It should be 85129597 instead of 81974060)
**The volume Macintosh HD was found corrupt and needs to be repaired.
Error: This disk needs to be repaired using the Recovery HD. Restart your computer,                 holding down the Command key and the R key until you see the Apple logo. When the Mac OS X Utilities window appears, choose Disk Utility.**

Do I need to follow the instructions at the bottom of the log? Is it necessary or can I forgo it? Thanks


It's not absolutely required, but I'd say it's strongly recommended. The type of volume corruption it reported isn't as serious as most other types, but my recommendation is the same: don't mess around, fix it now.

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File system corruption

In an edge case (say, a hard disk drive with a defective sector used by a critical part of the file system structure (extents overflow B-tree, catalog B-tree, attributes B-tree and more)):

  • a repair by fsck_hfs might do more harm than good, because drive-controlled reallocation of blocks may result in dataloss.

If you're lucky – most people are – then fsck_hfs without attention to media is the simplest and most appropriate course of action. So at the file system level (HFS Plus, in this case JHFS+) the recommended action is almost indisputable.

Storage system corruption

As Core Storage is closed source with too little information published by Apple, it's less clear what should be done about newer non-checkpoint transactions:

Hint: with Disk Utility, apparently OK is not always OK.

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