hspace
NAME
hspace - Cluster space analyzer for Ganeti
SYNOPSIS
hspace {backend options...} [algorithm options...] [request options...]
[output options...] [-v... | -q]
hspace –version
Backend options:
{ -m cluster | -L[ path ] | -t data-file |
–simulate spec | -I path }
Algorithm options:
[ –max-cpu *cpu-ratio* ]
[ –min-disk *disk-ratio* ]
[ -O *name...* ]
[ –independent-groups ]
Request options:
[–disk-template template ]
[–standard-alloc disk,ram,cpu ]
[–tiered-alloc disk,ram,cpu ]
Output options:
[–machine-readable**[=*CHOICE*] **]
[-p**[*fields*]]**
DESCRIPTION
hspace computes how many additional instances can be fit on a cluster,
while maintaining N+1 status.
The program will try to place instances, all of the same size, on the
cluster, until the point where we don’t have any N+1 possible
allocation. It uses the exact same allocation algorithm as the hail
iallocator plugin in allocate mode.
The output of the program is designed either for human consumption (the
default) or, when enabled with the --machine-readable option
(described further below), for machine consumption. In the latter case,
it is intended to interpreted as a shell fragment (or parsed as a
key=value file). Options which extend the output (e.g. -p, -v) will
output the additional information on stderr (such that the stdout is
still parseable).
By default, the instance specifications will be read from the cluster;
the options --standard-alloc and --tiered-alloc can be used to
override them.
The following keys are available in the machine-readable output of the
script (all prefixed with HTS_):
- SPEC_MEM, SPEC_DSK, SPEC_CPU, SPEC_RQN, SPEC_DISK_TEMPLATE, SPEC_SPN
- These represent the specifications of the instance model used for
allocation (the memory, disk, cpu, requested nodes, disk template,
spindles).
- TSPEC_INI_MEM, TSPEC_INI_DSK, TSPEC_INI_CPU, ...
- Only defined when the tiered mode allocation is enabled, these are
similar to the above specifications but show the initial starting spec
for tiered allocation.
- CLUSTER_MEM, CLUSTER_DSK, CLUSTER_CPU, CLUSTER_NODES, CLUSTER_SPN
- These represent the total memory, disk, CPU count, total nodes, and
total spindles in the cluster.
- INI_SCORE, FIN_SCORE
- These are the initial (current) and final cluster score (see the hbal
man page for details about the scoring algorithm).
- INI_INST_CNT, FIN_INST_CNT
- The initial and final instance count.
- INI_MEM_FREE, FIN_MEM_FREE
- The initial and final total free memory in the cluster (but this
doesn’t necessarily mean available for use).
- INI_MEM_AVAIL, FIN_MEM_AVAIL
- The initial and final total available memory for allocation in the
cluster. If allocating redundant instances, new instances could
increase the reserved memory so it doesn’t necessarily mean the
entirety of this memory can be used for new instance allocations.
- INI_MEM_RESVD, FIN_MEM_RESVD
- The initial and final reserved memory (for redundancy/N+1 purposes).
- INI_MEM_INST, FIN_MEM_INST
- The initial and final memory used for instances (actual runtime used
RAM).
- INI_MEM_OVERHEAD, FIN_MEM_OVERHEAD
- The initial and final memory overhead, i.e. memory used for the node
itself and unaccounted memory (e.g. due to hypervisor overhead).
- INI_MEM_EFF, HTS_INI_MEM_EFF
- The initial and final memory efficiency, represented as instance
memory divided by total memory.
- INI_DSK_FREE, INI_DSK_AVAIL, INI_DSK_RESVD, INI_DSK_INST, INI_DSK_EFF
- Initial disk stats, similar to the memory ones.
- FIN_DSK_FREE, FIN_DSK_AVAIL, FIN_DSK_RESVD, FIN_DSK_INST, FIN_DSK_EFF
- Final disk stats, similar to the memory ones.
- INI_SPN_FREE, ..., FIN_SPN_FREE, ..
- Initial and final spindles stats, similar to memory ones.
- INI_CPU_INST, FIN_CPU_INST
- Initial and final number of virtual CPUs used by instances.
- INI_CPU_EFF, FIN_CPU_EFF
- The initial and final CPU efficiency, represented as the count of
virtual instance CPUs divided by the total physical CPU count.
- INI_MNODE_MEM_AVAIL, FIN_MNODE_MEM_AVAIL
- The initial and final maximum per-node available memory. This is not
very useful as a metric but can give an impression of the status of
the nodes; as an example, this value restricts the maximum instance
size that can be still created on the cluster.
- INI_MNODE_DSK_AVAIL, FIN_MNODE_DSK_AVAIL
- Like the above but for disk.
- TSPEC
- This parameter holds the pairs of specifications and counts of
instances that can be created in the tiered allocation mode. The
value of the key is a space-separated list of values; each value is of
the form memory,disk,vcpu,spindles=count where the memory, disk and vcpu are
the values for the current spec, and count is how many instances of
this spec can be created. A complete value for this variable could be:
4096,102400,2,1=225 2560,102400,2,1=20 512,102400,2,1=21.
- KM_USED_CPU, KM_USED_NPU, KM_USED_MEM, KM_USED_DSK
- These represents the metrics of used resources at the start of the
computation (only for tiered allocation mode). The NPU value is
“normalized” CPU count, i.e. the number of virtual CPUs divided by
the maximum ratio of the virtual to physical CPUs.
- KM_POOL_CPU, KM_POOL_NPU, KM_POOL_MEM, KM_POOL_DSK
- These represents the total resources allocated during the tiered
allocation process. In effect, they represent how much is readily
available for allocation.
- KM_UNAV_CPU, KM_POOL_NPU, KM_UNAV_MEM, KM_UNAV_DSK
- These represents the resources left over (either free as in
unallocable or allocable on their own) after the tiered allocation
has been completed. They represent better the actual unallocable
resources, because some other resource has been exhausted. For
example, the cluster might still have 100GiB disk free, but with no
memory left for instances, we cannot allocate another instance, so
in effect the disk space is unallocable. Note that the CPUs here
represent instance virtual CPUs, and in case the –max-cpu option
hasn’t been specified this will be -1.
- ALLOC_USAGE
- The current usage represented as initial number of instances divided
per final number of instances.
- ALLOC_COUNT
- The number of instances allocated (delta between FIN_INST_CNT and
INI_INST_CNT).
- ALLOC_FAIL*_CNT
- For the last attemp at allocations (which would have increased
FIN_INST_CNT with one, if it had succeeded), this is the count of
the failure reasons per failure type; currently defined are FAILMEM,
FAILDISK and FAILCPU which represent errors due to not enough
memory, disk and CPUs, and FAILN1 which represents a non N+1
compliant cluster on which we can’t allocate instances at all.
- ALLOC_FAIL_REASON
- The reason for most of the failures, being one of the above FAIL*
strings.
- OK
- A marker representing the successful end of the computation, and
having value “1”. If this key is not present in the output it means
that the computation failed and any values present should not be
relied upon.
Many of the INI_/FIN_ metrics will be also displayed with a
TRL_ prefix, and denote the cluster status at the end of the tiered
allocation run.
The human output format should be self-explanatory, so it is not
described further.
OPTIONS
The options that can be passed to the program are as follows:
- –disk-template template
- Overrides the disk template for the instance read from the cluster;
one of the Ganeti disk templates (e.g. plain, drbd, so on) should be
passed in.
- –spindle-use spindles
- Override the spindle use for the instance read from the cluster. The
value can be 0 (for example for instances that use very low I/O), but not
negative. For shared storage the value is ignored.
- –max-cpu=*cpu-ratio*
- The maximum virtual to physical cpu ratio, as a floating point number
greater than or equal to one. For example, specifying cpu-ratio as
2.5 means that, for a 4-cpu machine, a maximum of 10 virtual cpus
should be allowed to be in use for primary instances. A value of
exactly one means there will be no over-subscription of CPU (except
for the CPU time used by the node itself), and values below one do not
make sense, as that means other resources (e.g. disk) won’t be fully
utilised due to CPU restrictions.
- –min-disk=*disk-ratio*
- The minimum amount of free disk space remaining, as a floating point
number. For example, specifying disk-ratio as 0.25 means that
at least one quarter of disk space should be left free on nodes.
- –independent-groups
- Consider all groups independent. That is, if a node that is not N+1
happy is found, ignore its group, but still do allocation in the other
groups. The default is to not try allocation at all, if some not N+1
happy node is found.
- –accept-existing-errors
- This is a strengthened form of –independent-groups. It tells hspace
to ignore the presence of not N+1 happy nodes and just allocate on
all other nodes without introducing new N+1 violations. Note that this
tends to overestimate the capacity, as instances still have to be
moved away from the existing not N+1 happy nodes.
- -l rounds, –max-length=*rounds*
- Restrict the number of instance allocations to this length. This is
not very useful in practice, but can be used for testing hspace
itself, or to limit the runtime for very big clusters.
- -p, –print-nodes
- Prints the before and after node status, in a format designed to allow
the user to understand the node’s most important parameters. See the
man page htools(1) for more details about this option.
- -O name
This option (which can be given multiple times) will mark nodes as
being offline. This means a couple of things:
- instances won’t be placed on these nodes, not even temporarily;
e.g. the replace primary move is not available if the secondary
node is offline, since this move requires a failover.
- these nodes will not be included in the score calculation (except
for the percentage of instances on offline nodes)
Note that the algorithm will also mark as offline any nodes which
are reported by RAPI as such, or that have ”?” in file-based input
in any numeric fields.
- -S filename, –save-cluster=*filename*
- If given, the state of the cluster at the end of the allocation is
saved to a file named filename.alloc, and if tiered allocation is
enabled, the state after tiered allocation will be saved to
filename.tiered. This allows re-feeding the cluster state to
either hspace itself (with different parameters) or for example
hbal, via the -t option.
- -t datafile, –text-data=*datafile*
- Backend specification: the name of the file holding node and instance
information (if not collecting via RAPI or LUXI). This or one of the
other backends must be selected. The option is described in the man
page htools(1).
- -m cluster
- Backend specification: collect data directly from the cluster given
as an argument via RAPI. The option is described in the man page
htools(1).
- -L [path]
- Backend specification: collect data directly from the master daemon,
which is to be contacted via LUXI (an internal Ganeti protocol). The
option is described in the man page htools(1).
- –simulate description
- Backend specification: similar to the -t option, this allows
overriding the cluster data with a simulated cluster. For details
about the description, see the man page htools(1).
- –standard-alloc disk,ram,cpu
This option overrides the instance size read from the cluster for the
standard allocation mode, where we simply allocate instances of the
same, fixed size until the cluster runs out of space.
The specification given is similar to the –simulate option and it
holds:
- the disk size of the instance (units can be used)
- the memory size of the instance (units can be used)
- the vcpu count for the insance
An example description would be 100G,4g,2 describing an instance
specification of 100GB of disk space, 4GiB of memory and 2 VCPUs.
- –tiered-alloc disk,ram,cpu
This option overrides the instance size for the tiered allocation
mode. In this mode, the algorithm starts from the given specification
and allocates until there is no more space; then it decreases the
specification and tries the allocation again. The decrease is done on
the metric that last failed during allocation. The argument should
have the same format as for --standard-alloc.
Also note that the normal allocation and the tiered allocation are
independent, and both start from the initial cluster state; as such,
the instance count for these two modes are not related one to
another.
- –machine-readable[=*choice*]
- By default, the output of the program is in “human-readable” format,
i.e. text descriptions. By passing this flag you can either enable
(--machine-readable or --machine-readable=yes) or explicitly
disable (--machine-readable=no) the machine readable format
described above.
- -v, –verbose
- Increase the output verbosity. Each usage of this option will
increase the verbosity (currently more than 2 doesn’t make sense)
from the default of one.
- -q, –quiet
- Decrease the output verbosity. Each usage of this option will
decrease the verbosity (less than zero doesn’t make sense) from the
default of one.
- -V, –version
- Just show the program version and exit.
UNITS
By default, all unit-accepting options use mebibytes. Using the
lower-case letters of m, g and t (or their longer equivalents of
mib, gib, tib, for which case doesn’t matter) explicit binary
units can be selected. Units in the SI system can be selected using the
upper-case letters of M, G and T (or their longer equivalents of
MB, GB, TB, for which case doesn’t matter).
More details about the difference between the SI and binary systems can
be read in the units(7) man page.
EXIT STATUS
The exist status of the command will be zero, unless for some reason
the algorithm fatally failed (e.g. wrong node or instance data).
BUGS
The algorithm is highly dependent on the number of nodes; its runtime
grows exponentially with this number, and as such is impractical for
really big clusters.
The algorithm doesn’t rebalance the cluster or try to get the optimal
fit; it just allocates in the best place for the current step, without
taking into consideration the impact on future placements.