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Re: [linux-lvm] Q: LVM over RAID, or plain disks? A:"Yes" = best of both worlds?



hansbkk gmail com wrote:
 - - - - - - My abject apologies to all for improper addressing in my
previous messages (thanks to all those who set me straight :)

Hope you're all still willing to consider my request for feedback.
Start with a bit of context:

- SAN/NAS (call it FILER-A) hosting say a dozen TB and servicing a few
dozen client machines and servers, mostly virtual hosts. Another,
larger (FILER-B - still just tens of TB) host's drives are used for
storing backup sets, via not only Amanda, but also filesystems
comprising gazillions of hard-linked archive sets created by (eg)
rdiff-backup, rsnapshot and BackupPC. We're on a very limited budget,
therefore no tape storage for backups.

- I plan to run LVM over RAID (likely RAID1 or RAID10) for IMO an
ideal combination of fault tolerance, performance and flexibility.

- I am not at this point overly concerned about performance issues -
reliability/redundancy and ease of recovery are my main priorities.


Problem:

For off-site data rotation, the hard-linked filesystems on FILER-B
require full filesystem cloning with block-level tools rather than
file-level copying or sync'ing. My current plan is to swap out disks
mirrored via RAID, marking them as "failed" and then rebuilding using
the (re-initialized) incoming rotation set.

HOWEVER - the use of LVM (and possibly RAID10) adds complexity to the
filesystems, which makes disaster recovery from the detached disk sets
much more difficult than regular partitions on physical disks.


Theoretical solution:

Use RAID1 on the "top layer" to mirror the data stored in an LVM (set
of) disk(s) on the one hand (call it TopRAID1) to ***regular
partitions*** on actual physical disks on the other (call this the
TopRAID2 side).

Your proposed solution is a bit confusing to understand, however raid1 works for doing backups in the manner that you describe . I use it myself and I have, over time read about others doing so as well. Be sure to create your volumes with --bitmap=internal, that way when you swap in a drive, it won't need to replicate the entire drive, only the part that is changed.

If your not going to manage the drives yourself, you will need an operations staff that has a pretty good understanding of how raid works and/or possibly write a robust set of scripts to manage the drives, ensure that the correct volume is mounted, etc. Also, I don't personally feel that disks are a suitable media for long term data archival, so if that is really your purpose, as opposed to a quick way to recover from a disk failure, then you might consider doing periodic tape or optical media backups as well.

Nataraj


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