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Manual Chapter: Share Farms
Manual Chapter
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Use the auto-migrate command to allow automatic migrations of files off of any share where the free space is too low.
The auto-migrate command allows the share farm to migrate files away from any of its shares who get too low on free space. The The policy freespace command sets the minimum free space to maintain at a given share. The policy engine migrates files off of the share to other shares in the same share farm, until the shares free space reaches or exceeds the resume-migrate threshold you set with the same policy freespace command.
This command migrates files that already exist in the share farm. To balance the distribution of newly-created files, use the balance command. This command only functions with balance capacity, which takes a shares free space into consideration when it distributes new files. This command cannot function in a share farm where constrain-files or constrain-directories are active; the constraints make auto migration impossible.
Use the show statistics migration command to monitor the file-migration activity in this share farm.
Use the balance command to balance all newly-created files amongst the shares in a share farm.
capacity distributes files to each share based on the shares current free space (capacity). If share A has twice as much free space as share B, it gets twice as many new files.
latency places more files in shares with low latency than shares with higher latency. Share latency is the average round-trip time from the ARX to the share; low latency is a sign of more available bandwidth between the switch and the share.
round-robin uses manually-configured weights to guide the distribution. If share A has a weight that is twice as high as share Bs weight, share A gets twice as many new files. You assign weight to a share when you add it to the share farm with share (gbl-ns-vol-sfarm).
To stop the distribution of new files, you can use constrain-files to constrain any new file to the same share as its parent directory. Additionally, you can use constrain-directories to keep directories with their parents. These constrain commands disable the effects of any balance command.
To activate balancing for the current share farm, use the enable (gbl-ns-vol-sfarm) command at the end of the command sequence. To stop balancing for the current share farm, use the no enable (gbl-ns-vol-sfarm) command, or invoke one of the constrain commands discussed above.
The auto-migrate command moves existing files off of a share if its free space drops too far. The auto-migrate command only functions if balance capacity is set, and you cannot set any other balance option if auto-migrate is enabled in this share farm.
Use the constrain-directories command to keep any newly-created directory on the same share as its parent. That is, the share that holds the parents master directory, for situations where the parent is striped on multiple shares in the volume.
depth (optional, integer 0-100) is the maximum depth of new directories that the share farm is allowed to balance. Below this directory depth, any new directory stays on the same share as its parent. This tends to preserve cohesive directory trees on back-end filers. For example, consider a volume that contains three directory trees, /a, /b, and /c: a share-farm with a depth of 1 could distribute the three directories to three separate shares, then keep the lower-level directories with their parents.
This limits or entirely disables the balance rule, which balances the placement of new files.
Use the constrain-files command to keep new files with their parent directories, too. If new files are not constrained and a client creates multiple files in the same directory, the balance rule is likely to distributes the files to multiple shares; to hold those files, it must replicate the directory in each share. This is called directory striping. In this situation, the constrain-directories command is choosing the share with the first (master) copy of the directory, but more copies are likely to exist.
Many installations use place-rules and age-filesets to implement tiered storage in a managed volume. For example, files modified in the past quarter are placed onto tier 1, and files that have gone unmodified for more than a quarter migrate down to tier 2. The tiers can be individual shares or they can be share farms. If they are share farms where constrain-files or constrain-directories is active, the volume uses an algorithm called share-farm mirroring to determine which share in the destination share farm gets the migrated subdirectory.
bstnA(gbl-ns-vol-sfarm[ns2~/usr~fm4])# constrain-directories below 1
Use the constrain files command to specify that new files be placed in the same shares as their parent directories. This reduces directory striping in the share farm; the share that has the master directory is typically the only share with any instance of the directory at all.
Use the no form of the command to remove the restriction and allow the balance rule to distribute files evenly throughout the current share farm.
This command enables you to restrict new-file placement to the same share as the parent directory. It disables the balance command with respect to files. This has no effect on the auto-migration of existing files, which is done to relieve a share that is running low on free space (see auto-migrate). Note that an auto migration has the side effect of creating stripe directories on other shares, but only when free space is running low.
You can also use the constrain-directories command to keep directories on the same share as their parents.
Many installations use place-rules and age-filesets to implement tiered storage in a managed volume. For example, files modified in the past week are placed onto tier 1, files modified last week are on tier 2, and files that have not been modified any time in the past 2 weeks are placed on tier 3. The tiers can be individual shares or they can be share farms. If they are share farms where constrain-files or constrain-directories is active, the volume uses an algorithm called share-farm mirroring to determine which share gets a file.
Use the enable command to enable the current rule. A new rule is disabled by default, and the policy engine ignores disabled rules.
Use no enable to disable the current rule.
Whenever any rule migrates a file to a share, it checks the shares free space against two thresholds. Each share has a minimum free space to maintain, as well as another (typically larger) level of free space called a resume threshold. If the file would reduce the shares free space below the maintain level, the rule waits until the free space rises to the resume level before migrating any more files to the share. The policy freespace command sets these free-space thresholds for an ARX share. Use this policy freespace command, from gbl-ns-vol-sfarm mode, to set the same thresholds for every share in the current share farm.
Use no policy freespace to return to the defaults for every share in the current share farm.
policy freespace maintain{k|M|G|T} resume-migrate resume{k|M|G|T}
policy freespace percent maintain-pct resume-migrate resume-pct
maintain is the amount of free space to maintain on these shares.
k|M|G|T chooses the unit of measure: kilobytes, Megabytes, Gigabytes, or Terabytes. A kilobyte is 1,024 bytes, a megabyte is 1,024 kilobytes (1,048,576 bytes), and so on..
resume is a free-space level for resuming migrations to any of these shares. The policy engine uses this value if one of the shares has reached its maintain value; no rule can migrate to such a share until its free space rises back to the resume level.
percent (optional) indicates that you are using disk-space percentages for these values instead of specific size measures.
maintain-pct (1-100) expresses the maintain value as a percentage of the overall share size.
resume-pct (1-100) is the resume threshold, expressed as a percentage of the shares total space.
resume - 2G
This is a macro command for the policy freespace command in gbl-ns-vol-shr mode. This command invokes the individual policy freespace command for every share in the current share farm. The output from show global-config shows the individual share-level policy freespace commands, not this macro command.
This is similar to the policy freespace (gbl-ns, gbl-ns-vol) command, a macro command for namespaces and volumes.
bstnA(gbl-ns-vol-sfarm[wwmed~/acct~fm1])# policy freespace 3G resume-migrate 4G
Use the share command from gbl-ns-vol-sfarm mode to add a managed volume share to the current share farm.
Use the no form of the command to delete a share from the share farm.
share name [weight weight]
name (1-64 characters) is the name of a share in the current managed volume. Use the show global-config namespace command for a list of configured shares.
weight (0 - 100) is the new-file-placement weight for the share. This number is proportional to other shares in the share farm; if one share has a 60 weight and another share has 30, the first share gets twice as many new files as the second. This weight is used with the balance round-robin rule; it is ignored for any other balance setting.
The no share command from gbl-ns-vol-sfarm mode does not delete the shares configuration; it only deletes the share from the share farm.
The order in which you invoke this command determines the ID of the share within the share farm. The first-added share has an ID of 1, the second has an ID of 2, and so forth. The share IDs are used for share-farm mirroring in a tiered volume; if a file migrates to a tier 3 share farm, its parents master directory is in the tier 1 share farm, and it is constrained to the same share as its parents master directory, the file goes to the share with the same ID as the parents master directory. The documentation for constrain-files and constrain-directories provides further details on share-farm mirroring.
If you remove the last share from the share farm with no share, other rules (such as a place-rule) can no longer use the share farm as a target for file migrations. The CLI prompts for confirmation if you attempt to remove the last share from the farm; enter yes to proceed.
Use the no form of the command to delete a share farm.
name (1-1024 characters) is the name you choose for the share farm.
When you create a new share farm, the CLI prompts for confirmation. Enter yes to create the share farm. (You can use terminal expert to eliminate confirmation prompts for creating new policy objects.)
This places you in gbl-ns-vol-sfarm mode, where you must use the share (gbl-ns-vol-sfarm) command to add at least one share to the farm. You can optionally use auto-migrate to migrate files off of any share that falls below a minimum amount of free space. The balance command distributes new files amongst the shares in the farm; you can weight this distribution based on current free space at each share (shares with more space get more new files), current latency at each share (shares with more bandwidth get more new files), or according to the weights you set with the share (gbl-ns-vol-sfarm) command. The latter form of the balance rule is active by default. To stop balancing new files, use the constrain-files and/or constrain-directories commands to keep any new file and/or directory on the same share as its parent directory.
Use show policy for details about a share farm and its policies. Use the show statistics migration command to monitor all migrations in the share farm.
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