[tahoe-dev] Fwd: Seeing some odd behavior

Shawn Willden shawn at willden.org
Thu Nov 3 14:09:27 UTC 2011


I sent this to tahoe-dev at allmydata.org the first time.  Oops.

---------- Forwarded message ----------
From: Shawn Willden <shawn at willden.org>
Date: Wed, Nov 2, 2011 at 7:40 AM
Subject: Seeing some odd behavior
To: tahoe-dev <tahoe-dev at allmydata.org>


I've been using "tahoe backup" to back up some of my data, but I've now
gotten through the low-volume, high-value stuff and am into the high-volume
moderate-value stuff so I decided to switch to using GridBackup (which I'm
also getting back to work on).

My theory has been that I could switch back and forth more or less with
impunity, since while the two tools use very different approaches for
storing metadata, both store the data files as immutable, and immutable
PUTs are idempotent in Tahoe.  As GridBackup tries to re-upload files which
are already in the grid, though, I'm seeing some odd behavior.

Specifically, files that have less than N shares in the grid are pushing
new shares -- but they're pushing too many.  My settings are 7/12/14 and
many files that already had 13 shares in the grid are pushing many new
shares, as many as 8 or 9.  Here's an example that pushed 5:

Upload Results

   - Shares Pushed: 5
   - Shares Already Present: 13
   - Sharemap:
      - 8 -> placed on [g4xvpwqa]
      - 9 -> placed on [kqyu52yz]
      - 10 -> placed on [kqlkvgiu]
      - 11 -> placed on [qivwuhf6]
      - 12 -> placed on [gbytbnxw]
   - Servermap:
      - [gbytbnxw] got share: #12
      - [g4xvpwqa] got share: #8
      - [kqlkvgiu] got share: #10
      - [kqyu52yz] got share: #9
      - [qivwuhf6] got share: #11
   - Timings:
      - File Size: 2158301 bytes
      - Total: 8.01s (269.5kBps)
         - Storage Index: 16ms (132.15MBps)
         - [Contacting Helper]:
            - [Helper Already-In-Grid Check]:
         - [Upload Ciphertext To Helper]: ()
         - Peer Selection: 4.73s
         - Encode And Push: 3.26s (845.7kBps)
            - Cumulative Encoding: 315ms (6.85MBps)
            - Cumulative Pushing: 2.24s (964.8kBps)
            - Send Hashes And Close: 616ms
         - [Helper Total]:


Can anyone explain why this would be?

Thanks,

-- 
Shawn.



-- 
Shawn
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