Extended attribute values can potentially be quite large. One test for ZFS is supposed to set a 200MB xattr. However, the buffer size for reading values from stdin with setextattr -i is so small that the test times out waiting for tiny chunks of data to be buffered and appended to an sbuf.
Increasing the buffer size should help alleviate some of the burden of reallocating larger sbufs when writing large extended attributes.
Sponsored by: iXsystems, Inc.