Okay, now, wait; are you saying that the storage device _does_ have a mechanism for communicating with the Linux filesystem to determine what filesystem pages are still cached in main storage and have not yet been commited to external storage?
J. Leslie Turriff VM Systems Programmer Central Missouri State University Room 400 Ward Edwards Building Warrensburg MO 64093 660-543-4285 660-580-0523 [EMAIL PROTECTED] >>>[EMAIL PROTECTED] 07/26/06 11:50 am >>> On Wednesday, 07/26/2006 at 10:33 EST, J Leslie Turriff <[EMAIL PROTECTED]> wrote: >Sounds to me, then, like the use of the >snapshot/mirror/peer-to-peer copy features of storage devices e.g. >Shark, SATABeast, etc. are currently dangerous to use with Linux >filesystems. They would need to be able to coordinate their activities >with the filesystem lock/unlock components of the kernel to be made >safe? No, they are not "currently dangerous to use with Linux". The snapshot/flashcopy features provide a point-in-time consistent view of an entire device or range of blocks/cylinders. In a "normal" track-by-track read, data on the device can change while you're reading. You're right, however, and as we've been discussing, that these features can be misused or misinterpreted to provide an -consistent view of the data. They don't do that. That applies to any operating system, not just Linux. And it's not the lock/unlock features of a filesystem that are important. Instead, the application must be able to exert control on the filesystem in such a way that it *knows* that all [relevant] data has been committed to disk and can say "OK. Now is a good time to take that backup." Properly used, these features can drastically reduce the amount of down time needed to perform application-consistent backups. Alan Altmark z/VM Development IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 !DSPAM:32225,44c79d9988571674117836! ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
