entries, which makes directory lookups and updates linear time operations and degrades performance on very large directories. The single B+ tree design in ReiserFS avoids both of these problems due to better scalability properties. Performance Compared with ext2 and ext3 in version 2.4 of the Linux kernel, when dealing with files under 4 KiB and with tail packing enabled, ReiserFS may be faster. Before Linux 2.6.33, ReiserFS heavily used the big kernel lock (BKL)—a global kernel-wide lock—which does not scale well for systems with multiple cores, as the critical code parts are only ever executed by one core at a time. Usage ReiserFS was the default file system in SuSE Linux since version 6.4 (released in 2000), until switching to ext3 in SUSE Linux Enterprise 10.2 and openSUSE 11, announced in 2006. Jeff Mahoney of SUSE wrote a post on 14 September 2006 proposing to move from ReiserFS to ext3 for the default installation file system. Some reasons he mentioned were scalability, "performance problems with extended attributes and ACLs", "a small and shrinking development community", and that "Reiser4 is not an incremental update and requires a reformat, which is unreasonable for most people." On October 4 he wrote a response comment on a blog in order to clear up some issues. He wrote that his proposal for the switch was unrelated to Hans Reiser being under trial for murder. Mahoney wrote he "was concerned that people would make a connection where none existed" and that "the timing is entirely coincidental and the motivation is unrelated." Criticism Some directory operations (including (2)) are not synchronous on ReiserFS, which can result in data corruption with applications relying heavily on file-based locks (such as mail transfer agents qmail and Postfix) if the machine halts before it has synchronized the disk. There are no programs to specifically defragment a ReiserFS file system, although tools have been written to automatically copy the contents of fragmented files hoping that more contiguous blocks of free space can be found. However, a "repacker" tool was planned for the next Reiser4 file system to deal with file fragmentation. Fragmentation is still an issue with SSD regardless of file system. fsck ReiserFS 3's fsck is capable to rebuild the whole tree as part of the rescue in case of its total corruption. This action has to be explicitly initiated by administrator and is not part of normal operation. Predictably, the