From: Daira Hopwood <daira@jacaranda.org>
Date: Thu, 5 Sep 2013 17:01:16 +0000 (+0100)
Subject: Sun May 13 22:07:39 BST 2012  Brian Warner <warner@lothar.com>
X-Git-Url: https://git.rkrishnan.org/components/architecture.txt?a=commitdiff_plain;h=a8f07df233d1f0dc6cdce4da0abc8134d1521a96;p=tahoe-lafs%2Ftahoe-lafs.git

Sun May 13 22:07:39 BST 2012  Brian Warner <warner@lothar.com>
  * performance.rst: small updates, mention (lack of) MDMF

  refs #1398
---

diff --git a/docs/performance.rst b/docs/performance.rst
index 4657c151..1766d381 100644
--- a/docs/performance.rst
+++ b/docs/performance.rst
@@ -28,6 +28,11 @@ written
 
 ``G`` indicates the number of storage servers on your grid
 
+Most of these cost estimates may have a further constant multiplier: when a
+formula says ``N/K*S``, the cost may actually be ``2*N/K*S`` or ``3*N/K*S``.
+Also note that all references to mutable files are for SDMF-formatted files;
+this document has not yet been updated to describe the MDMF format.
+
 Publishing an ``A``-byte immutable file
 =======================================
 
@@ -210,10 +215,15 @@ cpu: variable, between ~A and ~N/K*A
 
 network: variable; between A and N/K*A
 
-memory footprint: (1+N/K)*S
+memory footprint (immutable): (1+N/K)*S
+              (SDMF mutable): (1+N/K)*A
 
 notes: To repair a file, Tahoe-LAFS downloads the file, and
 generates/uploads missing shares in the same way as when it initially
 uploads the file.  So, depending on how many shares are missing, this
 can cost as little as a download or as much as a download followed by
 a full upload.
+
+Since SDMF files have only one segment, which must be processed in its
+entirety, repair requires a full-file download followed by a full-file
+upload.