StorNext snpolicyd Policies

You can create and edit StorNext snpolicyd policies from the StorNext GUI or with the snpolicy command. These snpolicyd policies differ from StorNext Storage Manager (SM) policies in several respects. Following is a summary of some of the similarities and differences between these two kinds of policies.

Storage Policy Option	Storage Manager Policy	snpolicyd Policy
Configurable via the StorNext GUI?	Yes. Select the Storage Policies menu’s Storage Manager option.	Yes. Select the Storage Policies menu’s Replication / Deduplication option.
Configurable via the command line?	Yes. Use fs commands such as `fsaddclass` and `fsmodclass`	Yes. Use the `snpolicy` command.
Where are policy internals stored?	In Storage Manager Database. One database per machine.	In the managed file system, in a private directory.
Is the policy used across file systems?	Yes. One policy can be used in multiple directories and multiple file systems.	No. Policies apply to one file system, but can be applied to multiple directories.
Functions?	Store (to tape or SDISK), retrieve, truncate files.	Deduplicate, replicate, truncate files.
How are truncated files retrieved?	The entire file must be retrieved.	Only portions of the file containing needed regions may be retrieved.
Schedules?	fspolicy / schedules stored in Database.	Linux crontab scheduling.
Management daemon?	multiple `fs_` processes	`snpolicyd`
Previous file versions recoverable?	Yes. Recover previous tape version with the `fsrecover` command. Up to 10 tape versions.	Yes. Previous replicated copies can be kept in previous replication directories. Up to 16.

Example

You create an snpolicyd policy with the StorNext GUI or with the snpolicy command. The snpolicy command is in directory /usr/cvfs/bin. Command line configuration must be done by the Linux root user.

Suppose you create directory /stornext/snfs1/photos in file system /stornext/snfs1 on machine host1. You then use the stornext GUI to create a replication policy named photo_rep to replicate this directory to file system /stornext/backup on machine host2. As in the previous example, the policy was configured to keep two copies on the target.

Now use the snpolicy command to see more internal details about the policy called photo_rep. Use the following command:

/usr/cvfs/config/snpolicy -dumppol/stornext/snfs1/photos

The command's output looks like the following:

inherit=photo_rep

key=1720399

root=/stornext/snfs1/photos

dedup=off

dedup_filter=off

max_seg_size=1G

max_seg_age=5m

dedup_age=1m

dedup_min_size=4K

dedup_seg_size=1G

dedup_min_round=8M

dedup_max_round=256M

dedup_bfst="localhost"

fencepost_gap=16M

trunc=off

trunc_age=365d

trunc_low_water=0

trunc_high_water=0

rep_output=true

rep_report=true

rep_target="target://stornext/backup@host2:"

rep_copies=2

There is a lot of output, most of which you do not have to consider. Some of the important values are:

inherit=photo_rep: This means the policy controlling this directory receives its parameters from the policy named photo_rep. Remember, when you create a policy you give it a name, and the policy name belongs to the file system. There could be a different policy named photo_rep in a different file system, and there would be no connection between the two photo_rep policies.
rep_output=true: This means the policy is a source of replication.
rep_copies=2: This means you want to keep two copies (instances) of the replicated directory on the target file system.
rep_target="target://stornext/backup@host2:": This tells you the replication target directory is a directory in file system
/stornext/backup on machine host2. But which directory name will be used in that file system? Since you did not specify anything else, the source directory name will be used. In this case the source directory name in the source file system is photos, so the target directory names will be /stornext/backup/photos and
/stornext/backup/photos.1.
dedup=off: This means the files in this directory are not deduplicated before being replicated. Deduplication and replication are discussed in another section.

One comment about a field not in the command output. Since there is no line for rep_input=true, this means this directory is not a replication target directory. This is not surprising. While it is true that a replication target can also be a replication source, that is an advanced case not covered here.