The layout of an attribute is 
offset(length)          Description
0(4)                    Type
4(2)                    Length
8(1)                    0=resident, 1=data stored in runs
9(1)                    name length
A(2)                    offset to name or resident data
C(2)                    1=compressed
E(2)                    Attribute ID
Resident attributes:
10(4)                  data length
14(2)                  offset to data
16(2)                  attribute is indexed
Nonresident attributes:
10(8)                   starting VCN of this segment
18(8)                   last VCN of this segment
20(2)                   offset to data
22(2?)                  Number of compression engine ? '4' for compressed files
28(8)                   allocated disk space
30(8)                   size of the attribute
38(8)                   length of initialized data
40(8)                   compressed size
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. The purpose of the indexed flag is unknown, as well as its presence for non-resident attributes.

For nonresident attributes, the data is stored in runs.