> From: Pascal Gienger > > STOP! > The capability to handle small files efficiently is related to the > filesystem carrying the files and NOT to the physical and logical > storage media (block device) under it. > > A SAN is a network where physical and logical block devices are shared > between nodes and which makes it possible to mount a harddisk or raid > partition as a block device even if the disk is some miles away - from > this point of view there is no difference between iSCSI (IP) and > FiberChannel > (FCP) besides different hardware. > > For your host/mail server there is no difference between having the > filesystem on - say - a 300 GB local hard drive partition or having it > on a SAN volume routed between SAN switches. The OS "sees" it like a > normal block device, and the filesystem just uses that. > > So if Apple says that Xsan does not handle many files they admit that > their > HFS+ file system is crap for many small files. That's just not true as a general statement. SAN is a broad term that applies to much more than just farming out block devices. Some of the more sophisticated SANs are filesystem-based, not block-based. This allows them to implement more advanced functionality like cross-platform sharing of volumes, simultaneous mounts of volumes from different hosts, backups (and single-file restores) performed by the SAN system, pooling of free space, transparent migration to offline storage, etc., etc., etc. Although I have no experience with it, it appears from a quick check of the web that Apple's XSAN indeed works that way and does not use HFS. So it's entirely credible for them to say that it is supported on a local filesystem but not XSAN, they are two different filesystems, not just different block devices. However, if you want to make a statement that the XSAN filesystem is crap for many small files, then that might be justified. Another instance of a SAN filesystem that I do happen to be familiar with is IBM's: http://www-03.ibm.com/servers/storage/software/virtualization/sfs/index.html David ---- Cyrus Home Page: http://asg.web.cmu.edu/cyrus Cyrus Wiki/FAQ: http://cyruswiki.andrew.cmu.edu List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
