mdadm - kernel - distro

1.12.0 - 2.6.15 - Ubuntu 6.06 LTS
2.5.6 - 2.6.20 - Ubuntu 7.04
2.6.3 - 2.6.24 - Ubuntu 8.04 LTS
2.6.7 - 2.6.27 - Ubuntu 8.10
2.6.7.1 - 2.6.28 - Ubuntu 9.04
1.12.0 - 2.6.9 - CentOS 4.5
2.5.4 - 2.6.18 - CentOS 5.0
2.5.6 - 2.6.18 - Debian 4.0r0
2.6.1 - 2.6.21 - Fedora 7

MDADM 2.x on kernels >2.6.17 supports online resizing of RAID 5 arrays