Managing zFS File Systems With the BPXWMIGF Migration Command
The BPXWMIGF command can now be used to non-disruptively manage your zFS file systems
By Daniel Acevedo11/18/2020
To enable administrators to migrate HFS file systems to zFS, z/OS® UNIX® System Services introduced the BPXWMIGF command in z/OS V2R3. The file system migration occurs in place without affecting any actively running workloads. In z/OS V2R4, BPXWMIGF was extended to support zFS to zFS migrations.
With the enhancements to BPXWMIGF in V2R4 to support zFS source file systems, you now have an easier way to manage your zFS file systems. You can allocate and use a new zFS file system data set without disruptions. You do not have to unmount your zFS file system when you move from one volume to another, make the file system bigger or change the key label of an encrypted file system.
BPXWMIGF copies all of the data from your source (old) file system to your target (new) file system, including access control lists (ACLs). It also maintains the same file identifiers (FIDs) for each node. BPXWMIGF is designed to work without affecting any running workloads. Any write type I/O that is occurring on the old file system is mirrored to the new file system to keep the two in sync. When the file system copy is complete, the new file system is swapped in place of the old file system without requiring an unmount. During this swap operation, all activity on the source file system is halted so that the source file system can be unmounted and the target file system mounted in its place. Any active operation on nodes within the file system will continue as though nothing had changed.
Let's take a look at a few examples.
bpxwmigf -source omvs.root.zfs -target omvs.root.new.zfs
In this example, OMVS.ROOT.ZFS is the source file system that will be migrated to target OMVS.ROOT.NEW.ZFS. By default, the swap will not occur once the copy is complete. To initiate the swap processing, you must use the -swap option. You have two choices when using the -swap option. You can use it on the original invocation of the BPXWMIGF command. Or, if you want to wait until later to initiate the swap, you can invoke the command again with the -swap option. During a migration, the mount mode and mount parameters are retained after the swap. If you want to automatically retain the same mount parameters, APAR OA58586 is required.
Let's say in our previous example that your source is mounted read/write and after you initiated the migration you decided that you would prefer to switch the mount mode to read-only after the migration is completed.
bpxwmigf -source omvs.root.zfs -mode ro -swap
BPXWMIGF is invoked again with the change in mount mode and we also decided to initiate the swap. You might think that you will have to update your BPXPRMxx parmlib member (or wherever else you reference the file system name) with the new name, but you don’t because BPXWMIGF has you covered there. You have options that allow you to rename the source and rename the target to the old source name or to just individually rename the source or target.
bpxwmigf -source omvs.root.zfs -target omvs.root.new.zfs -swap -srename omvs.root.old.zfs -trename
In the previous example, the source was renamed to OMVS.ROOT.OLD.ZFS and the target was renamed to the source's previous name, OMVS.ROOT.ZFS. Notice that the -swap option was used there. After all the data is copied, the swap starts and the file system data sets are renamed. All you had to do was use one single command to accomplish the renaming. No other changes were needed.
In order to keep track of everything, you can use the BPXWMIGF command to query the migrations. You can query a specific migration or all migrations, and you can filter by status (active/success/failed).
bpxwmigf -query omvs.root.zfs
Instead of specifying the -source option, you specify -query followed by the source file system. If you started a migration by mistake or decided that your target needed to be allocated with a different option, you can cancel the migration. Similar to querying, instead of using the -source option, you specify the
-cancel option with just the source file system's name specified.
bpxwmigf -cancel omvs.root.zfs
Before you start a migration, be aware of these usage notes:
- A move or unmount of the file system being migrated will cause the migration to be canceled.
- The target file system must be newly formatted. You cannot restart a failed or canceled migration. Instead, you must reformat the target and start the migration again.
- zFS to zFS migrations are supported in V2R4 and later. Previous releases cannot be in the SYSBPX sysplex group during the migration.
- Support for source file systems mounted as RWSHARE was provided via APAR OA57021.
Learn more about the BPXWMIGF command.
Daniel Acevedo is the z/OS UNIX File Systems product owner.
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