| mfsscadmin(1) | This is part of MooseFS | mfsscadmin(1) |
mfsscadmin - MooseFS storage class administration tool
mfsscadmin [/MOUNTPOINT] create|make [-a admin_only] [-m mode] [-C CREATION_LABELS] -K KEEP_LABELS [-A ARCH_LABELS -d ARCH_DELAY] SCLASS_NAME...
mfsscadmin [/MOUNTPOINT] create|make [-a admin_only] [-m mode] LABELS SCLASS_NAME...
mfsscadmin [/MOUNTPOINT] change|modify [-f] [-a admin_only] [-m mode] [-C CREATION_LABELS] [-K KEEP_LABELS] [-A ARCH_LABELS] [-d ARCH_DELAY] SCLASS_NAME...
mfsscadmin [/MOUNTPOINT] delete|remove SCLASS_NAME...
mfsscadmin [/MOUNTPOINT] copy|duplicate SRC_SCLASS_NAME DST_SCLASS_NAME...
mfsscadmin [/MOUNTPOINT] rename SRC_SCLASS_NAME DST_SCLASS_NAME
mfsscadmin [/MOUNTPOINT] list [-l]
mfsscadmin is a tool for defining storage classes, which can be later applied to MooseFS objects with mfssetsclass, mfsgetsclass etc. Storage class is a set of labels expressions and options that indicate, on which chunkservers the files in this class should be written and later kept.
create|make creates a new storage class with given options, described below and names it SCLASS_NAME; there can be more than one name provided, multiple storage classes with the same definition will be created then
change|modify changes the given options in a class or classes indicated by SCLASS_NAME parameter(s)
delete|remove removes the class or classes indicated by SCLASS_NAME parameter(s); if any of the classes is not empty (i.e. it is still used by some MooseFS objects), it will not be removed and the tool will return an error and an error message will be printed; empty classes will be removed in any case
copy|duplicate copies class indicated by SRC_SCLASS_NAME under a new name provided with DST_SCLASS_NAME
rename changes the name of a class from SRC_SCLASS_NAME to DST_SCLASS_NAME
list lists all the classes
-C optional parameter, that tells the system to which chunkservers, defined by the CREATION_LABELS expression, the chunk should be first written just after creation; if this parameter is not provided for a class, the KEEP_LABELS chunkservers will be used
-K mandatory parameter (assumed in the second, abbreviated version of the command), that tells the system on which chunkservers, defined by the KEEP_LABELS expression, the chunk(s) should be kept always, except for special conditions like creating and archiving, if defined
-A optional parameter, that tells the system on which chunkservers, defined by the ARCH_LABELS expression, the chunk(s) should be kept for archiving purposes; the system starts to treat a chunk as archive, when the last modification time of the file it belongs to is older than the number of days specified with -d option
-d optional parameter that MUST be defined when -A is defined, ARCH_DELAY parameter defines after how many days from last modification time a file (and its chunks) are treated as archive
-a can be either 1 or 0 and indicates if the storage class is available to everyone (0) or admin only (1)
-f force the changes on a predefined storage class (see below), use with caution!
-m is described below in CREATION MODES section
-l list also definitions, not only the names of existing storage classes
Labels are letters (A-Z - 26 letters) that can be assigned to chunkservers. Each chunkserver can have multiple (up to 26) labels. Labels are defined in mfschunkserver.cfg file, for more information refer to the appropriate manpage.
Labels expression is a set of subexpressions separated by commas, each subexpression specifies the storage schema of one copy of a file. Subexpression can be: an asterisk or a label schema. Label schema can be one label or an expression with sums, multiplications and brackets. Sum means a file can be stored on any chunkserver matching any element of the sum (logical or). Multiplication means a file can be stored only on a chunkserver matching all elements (logical and). Asterisk means any chunkserver. Identical subexpressions can be shortened by adding a number in front of one instead of repeating it a number of times.
Examples of labels expressions:
A,B - files will have two copies, one copy will be stored on chunkserver(s) with label A, the other on chunkserver(s) with label B
A,* - files will have two copies, one copy will be stored on chunkserver(s) with label A, the other on any chunkserver(s)
*,* - files will have two copies, stored on any chunkservers (different for each copy)
AB,C+D - files will have two copies, one copy will be stored on any chunkserver(s) that has both labels A and B (multiplication of labels), the other on any chunkserver(s) that has either the C label or the D label (sum of labels)
A,B[X+Y],C[X+Y] - files will have three copies, one copy will be stored on any chunkserver(s) with A label, the second on any chunserver(s) that has the B label and either X or Y label, the third on any chunkserver(s), that has the C label and either X or Y label
A,A expression is equivalent to 2A expression
A,BC,BC,BC expression is equivalent to A,3BC expression
*,* expression is equivalent to 2* expression is equivalent to 2 expression
It is important to specify what to do when it is not possible to meet the labels requirement of a storage class, i.e.: there is no space available on all servers with needed labels, there is not enough servers with needed labels or servers with needed labels are all busy. The question is if the system should create chunks on other servers (with non-matching labels) or not. This decision must be made by the user and hence the -m option.
In DEFAULT mode (no option or option -m D) in case of overloaded servers the system will wait for them, but in case of no space available it will use other servers and will replicate data to correct servers when it becomes possible. This means if some servers are in busy state for a long time, it might not be possible to create new chunks with certain storage classes and endangered (undergoal) chunks from those classes are at higher risk of being completely lost due to delayed replications.
Option -m S turns on STRICT mode. In this mode, during writing a new file, the system will return error (ENOSPC) in case of no space available on servers marked with labels specified for chunk creation. It will still wait for overloaded servers. Undergoal repliactions will not be performed if there is no space on servers with labels matching the storage class. This means high risk of losing data if servers with some labels are permamently filled up with data!
Option -m L turns on LOOSE mode. In this mode the system will immediately use other servers in case of overloaded servers or no space on servers and will replicate data to correct servers when it becomes possible. There is no delay or error on file creation and undergoal replications are always done as soon as possible.
This table sums up the modes:
| DEFAULT | STRICT | LOOSE | |
| CREATE - BUSY | WAIT | WAIT | WRITE ANY |
| CREATE - NO SPACE | WRITE ANY | ENOSPC | WRITE ANY |
| REPLICATE - BUSY | WAIT | WAIT | WRITE ANY |
| REPLICATE - NO SPACE | WRITE ANY | NO COPY | WRITE ANY |
For compatibility reasons, every fresh or freshly upgraded instance of MooseFS has 9 predefined storage classes. Their names are single digits, from 1 to 9, and their definitions are * to 9*. They are equivalents of simple numeric goals from previous versions of the system. In case of an upgrade, all files that had goal N before upgrade, will now have N storage class. These classes can be modified only when option -f is specified. It is advised to create new storage classes in an upgraded system and migrate files with mfsxchgsclass tool, rather than modify the predefined classes. The predefined classes CANNOT be deleted nor renamed.
Report bugs to <bugs@moosefs.com>.
Copyright (C) 2023 Jakub Kruszona-Zawadzki, Saglabs SA
This file is part of MooseFS.
MooseFS is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2 (only).
MooseFS is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with MooseFS; if not, write to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02111-1301, USA or visit http://www.gnu.org/licenses/gpl-2.0.html
mfsmount(8), mfstools(1), mfssclass(1), mfschunkserver.cfg(5)
| February 2023 | MooseFS 3.0.117-1 |