jhfs+ question, jhdr size
jhfs+ question, jhdr size
- Subject: jhfs+ question, jhdr size
- From: Chris Murphy <email@hidden>
- Date: Sat, 04 Feb 2012 11:25:07 -0700
I'm finding a discrepancy between available (legacy) documentation regarding jhdr_size and reality on large disks, equal to or greater than 2TB.
> https://developer.apple.com/legacy/mac/library/#technotes/tn/tn1150.html
>
> jhdr_size
> The size of the journal header, in bytes. The journal header always occupies exactly one sector so that it can be updated atomically. Therefore, this value is equal to the sector size (for example, 2048 on many types of optical media).
However, I'm finding on at least 2+TB disks, the jhdr_size is not 512 bytes, but rather 4096 bytes. This is with real physical disks as well as virtual disks, neither of which are 4Kn disks. When the disk is at or below 1TB in size, the jhdr_size is 512. So somewhere in between 1TB and 2TB, jhdr_size jumps to 4096, being apparently related to disk or volume size, rather than sector size as documentation states.
So I'm wondering if something has changed and if there is newer documentation that describes the expected behavior?
Thanks,
Chris Murphy
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