On 11/30/2010 11:45 PM, hansbkk@xxxxxxxxx wrote: > On Tue, Nov 30, 2010 at 11:56 PM, Phil Turmel <philip@xxxxxxxxxx> wrote: > >> (Actually, rsync and tar are both hardlink-aware, at least the versions I use.) > > My backup filesystems contain so many hardlinks (millions, constantly > growing) that file-level tools choke - this really must be done at the > block device level - see my previous post for more detail. Ah -- I did miss that detail. > It's also now clear to me that rsync is the tool to use for this for > all the other LVs without such problematic filesystems, as I know the > tool and trust its error-checking routines. Indeed. I push my own critical systems offsite with rsync+ssh. [snip /] >> I would use dd. > > OK, that's clear, thanks. > > >> You want your dismountable disks to be accessible stand-alone, but I don't see why that would preclude setting them up so each is a unique LVM VG. > > It doesn't preclude it, but it's a layer of complexity during the data > recovery process I'm trying to avoid. > > The ultimate goal is a plain partition on a plain disk that can be > directly mounted on a SATA2 host via a normal recovery/LiveCD by a > user that's never heard of RAID or LVM. Ah -- not *you*. And you wouldn't be mixing customers on a disk, I presume? > To summarize your feedback: > > - mdraid's sync error-checking routines don't add value over dd to > ensure accurate cloning of a static partition; its metadata is just > useless overhead in this case. Right. > - dd is reliable enough I guess if your filer lacks ECC ram, you could have a bit flip between reading and writing that would be missed. It's really an end-to-end hardware integrity issue at this level. But an undetected read error between the platter and RAM will be propagated by every block-level software tool out there, including software raid. btrfs can do data-checksumming, but that's at the FS level. > One last question (and I do realize it's now OT for here, so I won't > be hurt if it's ignored :) > > Does dd already do some sort of "verify after copy"? I will likely > investigate the available COTS partition cloning tools as well. Not natively, but it fairly easy to pipe a dd reader through md5sum to a dd writer, then follow up with a dd read + md5sum of the copied partition (taking care to read precisely the same number of sectors). The various flavors of ddrescue might have something like this.. didn't check. > Thanks for all your help, not least in helping me to clarify my own goals You're welcome. Phil -- 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
