1 .TH HN1 1 2009-03-14 htools "Ganeti H-tools"
3 hn1 \- N+1 fixer for Ganeti
10 .BI "[ -m " cluster "]"
11 .BI "[-n " nodes-file " ]"
12 .BI "[ -i " instances-file "]"
14 .BI "[-r " max-removals "]"
15 .BI "[-L " max-delta "]"
16 .BI "[-l " min-delta "]"
22 hn1 is a cluster N+1 fixer that tries to compute the minimum number of
23 moves needed for getting all nodes to be N+1 compliant.
25 The algorithm is designed to be a 'perfect' algorithm, so that we
26 always examine the entire solution space until we find the minimum
27 solution. The algorithm can be tweaked via the \fB-d\fR, \fB-r\fR,
28 \fB-L\fR and \fB-l\fR options.
30 By default, the program will show the solution in a somewhat cryptic
31 format; for getting the actual Ganeti command list, use the \fB-C\fR
34 \fBNote:\fR this program is somewhat deprecated; \fBhbal(1)\fR gives
35 usually much faster results, and a better cluster. It is recommended
36 to use this program only when \fBhbal\fR doesn't give a N+1 compliant
41 The algorithm works in multiple rounds, of increasing \fIdepth\fR,
42 until we have a solution.
44 First, before starting the solution computation, we compute all the
45 N+1-fail nodes and the instances they hold. These instances are
46 candidate for replacement (and only these!).
48 The program start then with \fIdepth\fR one (unless overridden via the
49 \fB-d\fR option), and at each round:
50 - it tries to remove from the cluster as many instances as the
51 current depth in order to make the cluster N+1 compliant
52 - then, for each of the possible instance combinations that allow
53 this (unless the total size is reduced via the \fB-r\fR option),
54 it tries to put them back on the cluster while maintaining N+1
57 It might be that at a given round, the results are:
58 - no instance combination that can be put back; this means it is not
59 possible to make the cluster N+1 compliant with this number of
60 instances being moved, so we increase the depth and go on to the
62 - one or more successful result, in which case we take the one that
63 has as few changes as possible (by change meaning a replace-disks
66 The main problem with the algorithm is that, being an exhaustive
67 search, the CPU time required grows very very quickly based on
68 depth. On a 20-node, 80-instances cluster, depths up to 5-6 are
69 quickly computed, and depth 10 could already take days.
71 Since the algorithm is designed to prune the search space as quickly
72 as possible, is by luck we find a good solution early at a given
73 depth, then the other solutions which would result in a bigger delta
74 (the number of changes) will not be investigated, and the program will
75 finish fast. Since this is random and depends on where in the full
76 solution space the good solution will be, there are two options for
77 cutting down the time needed:
78 - \fB-l\fR makes any solution that has delta lower than its
79 parameter succeed instantly
80 - \fB-L\fR makes any solution with delta higher than its parameter
81 being rejected instantly (and not descend on the search tree)
84 The options that can be passed to the program are as follows:
86 .B -C, --print-commands
87 Print the command list at the end of the run. Without this, the
88 program will only show a shorter, but cryptic output.
91 Prints the before and after node status, in a format designed to allow
92 the user to understand the node's most important parameters.
94 The node list will contain these informations:
95 - a character denoting the status of the node, with '-' meaning an
96 offline node, '*' meaning N+1 failure and blank meaning a good
99 - the total node memory
100 - the free node memory
101 - the reserved node memory, which is the amount of free memory
102 needed for N+1 compliance
105 - number of primary instances
106 - number of secondary instances
107 - percent of free memory
108 - percent of free disk
111 .BI "-n" nodefile ", --nodes=" nodefile
112 The name of the file holding node information (if not collecting via
113 RAPI), instead of the default
118 .BI "-i" instancefile ", --instances=" instancefile
119 The name of the file holding instance information (if not collecting
120 via RAPI), instead of the default
126 Collect data not from files but directly from the
128 given as an argument via RAPI. This work for both Ganeti 1.2 and
132 .BI "-d" DEPTH ", --depth=" DEPTH
133 Start the algorithm directly at depth \fID\fR, so that we don't
134 examine lower depth. This will be faster if we know a solution is not
135 found a lower depths, and thus it's unneeded to search them.
138 .BI "-l" MIN-DELTA ", --min-delta=" MIN-DELTA
139 If we find a solution with delta lower or equal to \fIMIN-DELTA\fR,
140 consider this a success and don't examine further.
143 .BI "-L" MAX-DELTA ", --max-delta=" MAX-DELTA
144 If while computing a solution, it's intermediate delta is already
145 higher or equal to \fIMAX-DELTA\fR, consider this a failure and abort
146 (as if N+1 checks have failed).
150 Just show the program version and exit.
154 The exist status of the command will be zero, unless for some reason
155 the algorithm fatally failed (e.g. wrong node or instance data).
159 The program does not check its input data for consistency, and aborts
160 with cryptic errors messages in this case.
162 The algorithm doesn't know when it won't be possible to reach N+1
163 compliance at all, and will happily churn CPU for ages without
164 realising it won't reach a solution.
166 The algorithm is too slow.
168 The output format is not easily scriptable, and the program should
169 feed moves directly into Ganeti (either via RAPI or via a gnt-debug
173 hbal(1), ganeti(7), gnt-instance(8), gnt-node(8)
projects / ganeti-local / blob