From: Brian Warner Date: Fri, 7 Sep 2007 06:01:07 +0000 (-0700) Subject: provisioning: explain the 'survival' number better X-Git-Url: https://git.rkrishnan.org/module-simplejson.decoder.html?a=commitdiff_plain;h=5561d3afe4011e94d40143d41bc8b025f8272ba3;p=tahoe-lafs%2Ftahoe-lafs.git provisioning: explain the 'survival' number better --- diff --git a/src/allmydata/provisioning.py b/src/allmydata/provisioning.py index b07c6b8e..ae0cd8a7 100644 --- a/src/allmydata/provisioning.py +++ b/src/allmydata/provisioning.py @@ -597,6 +597,13 @@ class ProvisioningTool(rend.Page): T.div["share data loss rate: ", number(share_data_loss_rate,"Bps")]) + # the worst-case survival numbers occur when we do a file check + # and the file is just above the threshold for repair (so we + # decide to not repair it). The question is then: what is the + # chance that the file will decay so badly before the next check + # that we can't recover it? The resulting probability is per + # check interval. + # Note that the chances of us getting into this situation are low. P_disk_failure_during_interval = (drive_failure_rate * file_check_interval) disk_failure_dBF = 10*math.log10(P_disk_failure_during_interval) @@ -614,6 +621,7 @@ class ProvisioningTool(rend.Page): user_files_survives_dBA, "all files in grid = %d dBA" % all_files_survives_dBA, + " (per worst-case check interval)", ])