Hi,

Jeffrey J. Kosowsky wrote on 2011-03-09 17:43:41 -0500 [Re: [BackupPC-users] 
Still trying to understand reason for extremely slow backup speed...]:
> [...] I actually used my program that I posted to copy
> it over and I checked that all the links are ok.

I believe you have changed more than four variables ;-). BackupPC, as we all
know, depends heavily on seek times. When you are measuring NFS speed, what
exactly *are* you measuring? Probably not what BackupPC is doing, so that may
or may not explain the difference. You said you "changed from ext2 to lvm2" -
I suppose you are still using a file system? ;-) And almost definitely a
different one, else you would have used dd ...

- LVM may or may not make the seeks slower. I wouldn't expect it. I suspect
  many people use BackupPC on LVM - for the flexibility of resizing the pool
  partition if nothing else. Mileage on ARM NAS devices may vary.
- The FS may or may not behave differently.
- The inode layout after copying may or may not be less efficient. Even
  significantly so. I can't tell you what a generically good order to create
  the copied files, directories, pool entries for a BackupPC pool (tm) would
  be, else I'd re-implement your program ;-). My understanding is that there
  is no "good" layout for a BackupPC pool, but there are bound to be varying
  degrees of bad layouts.
- In theory, RAID1 might have eliminated many of the seeks (on reading, that
  is), if the usage pattern of the pool and the driver implementation happen
  to fit. Might be interesting to figure out how many mirrors and what hard-
  or software raid would be optimal for BackupPC ;-). But that's a 3.x topic.

Does the backup "sound" seek-limited, or is the NAS disk idle some of the
time? You didn't also change NFS mount options, did you ;-?

Is at least as much memory available (for disk cache, if that's not obvious)
on the NAS as before the kernel upgrade? Does the NAS swap? Is it swapping?

I can't think of any more questions to ask right now. Good luck :).

Regards,
Holger

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