On Fri, Sep 12, 2008 at 7:43 PM, FUJITA Tomonori <fujita.tomonori at lab.ntt.co.jp> wrote: > On Fri, 12 Sep 2008 19:34:00 +1000 > "ronnie sahlberg" <ronniesahlberg at gmail.com> wrote: > >> This is a feature that all enterprise targets support. > > Can you tell me what feature you are talking about? > > Sounds like you are taking something like SnapMirror (in NetApp term). > I am talking about STD (pruduction lun) BCV (mirror) and ESTABLISH (the operation to attach and sync the BCV to the STD) and SPLIT (the operation to disconnect it again so it becomes a "snapshot) in emc terminology. So a workflow for backup would be 1, ESTABLISH BCV to STD, 2, wait until the BCV is fully synchronized 3, SPLIT the BCV off the STD 4, export the BCV to a different host B 5, on host B, mount the BCV and do an incremental backup of the data 6, unmount the BCV from host B 7, goto 1 This is a normal sequence on how to do backups on a production system. The purpose is so that the backups can be performed by a separate host using separate spindles from the production lun so that there is no impact to performance to access the pruduction lun while performing the backup. The STD is always the master so after the BCV has been ESTABLISHED to the STD again, the BCV becomes an identical copy of the STD. This means that all changes made to the STD since the last SPLIT will have to be merged onto the BCV. It also means that if there were changes done to the BCV after the split, these changes must be discarded and these blocks must also be merged from the STD onto the BCV. This is the normal mode. Where you always merge from STD onto BCV so the BCV becomes identical to the STD. If using a BCV as the actual backup itself, in that case one also need a mechanism to do a reverse merge, that is to ESTABLISH the BCV with the STD again but this time they are merged so that the STD becomes identical to the BCV. In both cases both devices need to keep a bitmap to track which blocks have changed since last SPLIT. The only difference is just the direction of the merge. >From or to STD. This would require a new backend for use with the sbc emulation but would be useful. I might hack on it in some future. -- To unsubscribe from this list: send the line "unsubscribe stgt" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html |