On Tue, Nov 30, 2010 at 8:13 PM, Phil Turmel <philip@xxxxxxxxxx> wrote: > I think you are making this overly complex, insisting on a RAID1 operation to backup from on filer to the other. Consider having each disk on filer #2 configured as a single LVM PV/VG, so it can stand alone in a rotation. The try the alternate below. <snip> > As an alternate, with simpler recovery semantics: > Create matching LV on non-RAID PV/VG on filer #2 > dd + netcat + dd or other technique to dup the snapshot on filer #1 to filer #2 > >> - delete the snapshot Thanks Phil, and yes I do tend to complicate things during a learning/planning stage, then when I get to implementation reality tends to force simplification :) Perhaps I miscommunicated, but your suggestion misses a couple of factors: - this process is (so far) only targeting the backup data hosted on Filer-B - the backup-mirroring I'm considering is all within that one server, not across a network connection - I can't have "each disk configured as a single VG", since the whole point of my using LVM is to get as much flexibility as possible for dozens of hosts to share my dozen-terabyte disk space, when I only have a half-dozen disks. - my goal is for the snapshot-copy to end up in a regular partition on a physical disk, without any RAID/LVM layers standing between the data and easy recovery However your main point is perfectly valid - dd basically does the same block-level data transfer as mdm RAID1 - which is a must for the gazillions-of-hardlinks backup filesystems (as opposed to file-level tools like rsync). So adapting your suggestion to fit (my perception of) my needs: - create an LV snapshot - mount a plain partition on a physical hard disk (preferably on a separate controller?) - dd the data from the LV snapshot over to the partition - delete the snapshot > A RAID mirror can only duplicate the raw block device. Isn't that all that dd is doing as well? My perception is that software like mdm, designed as it is to maximize data reliability would handle the cloning more reliably than dd - isn't there more error-checking going on during a RAID1 re-mirroring? Your main (and quite valid) point is that a user-space tool designed to do the job is probably more appropriate than putting RAID1 to use in a way beyond what was originally intended. So I guess my question becomes: What is the best tool to block-level clone an LV snapshot to a regular disk partition? - "best" = as close to 100% reliably as possible, speed isn't nearly as important Would a COT cloning package (something like Acronis TrueImage) have data reliability advantages (like mdm's) over dd? -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
