How about we don't generalize "soft raid is better," "hard raid is better," ... No, emacs is better, no vi is better. No, star wars is better, No star trek is better, No LOTR is better. ;-)
Hard vs Soft raid being better... This is largely dependent on the hardware and software. In ZFS, for example, you really want the software raid, provided you have an SSD for ZIL. It outperforms the hw raid because it has knowledge of the block level and filesystem level objects, so it's able to reorganize them, aligning small writes into larger sequential writes to gain performance. Plus, since it's doing the checksumming, it actually *needs* access to the redundant data in order to correct problems when it finds them. Due to this intelligence, and an always-consistent on-disk format, there is no need for the BBU cache, in fact, the BBU cache hurts performance. So you get optimum performance, reliability, and compatibility by eliminating the HW raid on ZFS. Again for emphasis: Provided you have SSD for ZIL. But if you don't have SSD for ZIL, then you're better using the BBU HBA rather than using nothing for write buffering. In windows, for example, you really want the hardware raid. Because the soft raid in windows causes system imaging problems and compatibility problems if you actually need to pull the disks out and attach to a different system. As mentioned by somebody else, without the BBU cache/buffer, the system can only buffer writes in memory that are safe to buffer in memory, but with the BBU, you gain performance because the hardware is doing the buffering and will survive even if the OS kernel blue-screens or you have power loss or something... Linux is somewhere in between. Some characteristics in linux are better with software raid, and some are better with hardware raid. In ext3/4, you gain performance by using the HW BBU cache/buffer (not sure if btrfs goes faster with/without the BBU HBA, I think btrfs also benefits from the BBU HBA). But in ext3/4 and btrfs, the extra hardware creates another possible compatibility problem and failure point, which some people would prefer to just eliminate. So. Software is better sometimes. Hardware is better sometimes. _______________________________________________ Tech mailing list [email protected] https://lists.lopsa.org/cgi-bin/mailman/listinfo/tech This list provided by the League of Professional System Administrators http://lopsa.org/
