Log-structured File System - Disadvantages

Disadvantages

The design rationale for log-structured file systems assumes that most reads will be optimized away by ever-enlarging memory caches. This assumption does not always hold:

• On magnetic media—where seeks are relatively expensive—the log structure may actually make reads much slower, since it fragments files that conventional file systems normally keep contiguous with in-place writes.
• On flash memory—where seek times are usually negligible—the log structure may not confer a worthwhile performance gain because write fragmentation has much less of an impact on write throughput. However many flash based devices cannot rewrite part of a block, and they must first perform a (slow) erase cycle of each block before being able to re-write, so by putting all the writes in one block, this can help performance as opposed to writes scattered into various blocks, each one of which must be copied into a buffer, erased, and written back.