Re: Kernel logging I/O Errors for Disk Images
Re: Kernel logging I/O Errors for Disk Images
- Subject: Re: Kernel logging I/O Errors for Disk Images
- From: Nick Blievers <email@hidden>
- Date: Wed, 07 Nov 2012 14:54:31 -0600
- Acceptlanguage: en-US
- Thread-topic: Kernel logging I/O Errors for Disk Images
On 08/11/2012, at 3:58 AM, Julian Mayer wrote:
>>
>> I can't answer all your questions, but can at least clarify some of it. Based on mount.h we can see what the events are:
>>
>> #define VQ_VERYLOWDISK 0x0200 /* file system has *very* little disk space left */
>> #define VQ_LOWDISK 0x0004 /* we're low on space */
>>
>> Which kind of makes sense, the disk image may not have very much free space, and this is probably generated on mount.
>
>
> hi
>
> i also suspected "low disk" might mean little space left, but i'm not sure it makes sense.
>
> all read-only disk images are generally sized-to-fit so they have exactly 0 bytes free. nevertheless i've never seen any warnings like this when mounting or using disk images.
>
> thanks, julian
Hi,
It is reproducible if the disk image is read-write (and has zero free space):
8/11/12 7:46:21.009 AM KernelEventAgent: tid 00000000 received event(s) VQ_LOWDISK, VQ_VERYLOWDISK (516)
8/11/12 7:46:21.012 AM KernelEventAgent: tid 00000000 type 'hfs', mounted on '/Volumes/otx', from '/dev/disk3', low disk, very low disk
8/11/12 7:46:21.000 AM kernel: HFS: Very Low Disk: freeblks: 0, dangerlimit: 10
You are correct in that readonly images don't (that I've seen anyway) produce this warning, but my guess is you have got hold of a rw image when you expected a ro one.
You can run hdiutil imageinfo to gather some information about the disk image:
$ hdiutil imageinfo `pwd`/test.dmg
Backing Store Information:
URL: file://tmp/test.dmg
Name: test.dmg
Class Name: CBSDBackingStore
Class Name: CRawDiskImage
Checksum Type: none
Size Information:
Total Bytes: 4194304
Compressed Ratio: 1
Sector Count: 8192
Total Non-Empty Bytes: 4194304
Compressed Bytes: 4194304
Total Empty Bytes: 0
Format: UDRW
Format Description: raw read/write
Checksum Value:
Properties:
Encrypted: false
Kernel Compatible: true
Checksummed: false
Software License Agreement: false
Partitioned: false
Compressed: no
Segments:
0: /Developer/Source/10.7.3/xnu-1699.24.23/test.dmg
partitions:
partition-scheme: none
block-size: 512
appendable: true
partitions:
0:
partition-name: whole disk
partition-start: 0
partition-synthesized: true
partition-length: 8192
partition-hint: Apple_HFS
partition-filesystems:
HFS+:
NTFS: UNTITLED
burnable: true
Resize limits (per hdiutil resize -limits):
min cur max
8192 8192 357871048
Note that this has a read/write format (UDRW) and has no free space.
Cheers
Nick
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