The layout of an attribute is
offset(length)          Description
0(4)                    Type
4(4)                    Length
8(1)                    0=resident, 1=data stored in runs
9(1)                    name length
A(1)                    offset to data. Might be at 0x20 as well
C(1)                    1=compressed
Resident attributes:
10(2?)                  data length
Nonresident attributes:
10(8)                   starting VCN of this segment
20(2)                   offset to data
18(8)                   last VCN of this segment
28(8)                   size of the attribute
30(8)                   allocated disk space
38(8)                   length of initialized data
All:
data start              Name (if present)
data start + namelen    start of data or data runs
The following attribute types are known. The list of attributes of a volume is stored in the $Attribute file. The data structure of the attributes 20,40,50,60,70,B0,C0,D0, and E0 is unknown.

For nonresident attributes, the data is stored in runs.