Dell EqualLogic PS6210XS EqualLogic Host Integration Tools for Linux Version 1 - Page 99

Group Access Files, Considerations for Thin-Provisioning, File System and Volume Characteristics

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Group Access Files Access to the PS Series groups by eqlvolume is controlled by entries in the group access file. These entries are built and maintained by the asmcli utility. For more information about group access files, use the asmcli help group-access command. Considerations for Thin-Provisioning Several characteristics are considered when eqlvolume determines whether or not a volume can be thin-provisioned. See the following sections for more information: • File System and Volume Characteristics • Multiple File Systems File System and Volume Characteristics The eqlvolume tool uses characteristics of the file system and the EqualLogic volume, as well as defined configuration parameters to determine if a volume can be rethinned. For information on the defined configuration parameters, see Volume Thin-Provisioning Configuration Parameters. File system characteristics that prevent eqlvolume from recommending rethinning include: • Read-only file system-A file system that is mounted as read-only cannot be updated, nor can space be allocated or deallocated. • Lack of FITRIM ioctl() or -o discard support-Thin-provisioning requires either FITRIM ioctl() or -o discard support. If a file system was not mounted with the -o discard option, eqlvolume might need to remount that file system using the -o discard option, perform on-demand thin-provisioning, and remount the file system with the -o nodiscard option. A file system that does not support -o nodiscard cannot be restored to its original state after thin-provisioning, and eqlvolume will not recommend that file system for on-demand thin-provisioning. • A gfs2 file system without FITRIM support-Thin-provisioning a gfs2 file system by allocating most of the disk space and deleting the temporary files is very slow, so eqlvolume does not recommend thin-provisioning a gfs2 files system without FITRIM. • Insufficient free space-Without sufficient free space in the file system, eqlvolume is unlikely to recover any significant free space on the volume. EqualLogic volume characteristics that prevent eqlvolume from recommending thin-provisioning include: • Target is a snapshot-Snapshots only store changes to the volume, so they are already space efficient. • Volume is not t1in-provisioned-If the volume is not thin-provisioned, space is preallocated to the volume, and free space cannot be recovered. • Firmware-Firmware in the PS Series group does not support unmaps, or discards. • Replication or synchronous replication is configured-Replicated volumes do not support thin-provisioning. • Volume is a replica failover volume-The product of a replicated volume is not a good candidate for thin-provisioning. Multiple File Systems If all of the characteristics of the file system and the volume indicate that on-demand thin-provisioning is possible, eqlvolume recommends thin-provisioning based on a comparison of the space used by the file systems and the volumes that support them. When eqlvolume evaluates multiple file systems built by multiple logical volumes from one or more target volumes or file systems built by partitions, the function compares the total amount of space used by all of the related file systems to the total amount of space used by the target volumes. If the space used by the target volumes is significantly greater than the space used by the file systems, all of the file systems are recommended for thin-provisioning because it is impossible to predict what free space was originally part of which file system. If a target volume supports multiple file systems through logical volumes or partitions, and one or more of those file systems are not mounted, eqlvolume cannot include the amount of space used by the unmounted file systems. In this circumstance, eqlvolume will likely recommend that the remaining file systems be thin-provisioned. For example, if two partitions (file systems) each use 100GB, and the target volume has 300 GB of space in use, eqlvolume will recommend that the two partitions be thin-provisioned. However, if a third partition is using 100 GB of space but is not mounted, the space used by the third (unmounted) partition can cause eqlvolume to recommend thin-provisioning, although the thin-provisioning will likely not recover any free space. Managing Thin-Provisioned Volumes 99

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Group Access Files
Access to the PS Series groups by eqlvolume is controlled by entries in the group access file. These entries are built and maintained by the
asmcli utility.
For more information about group access files, use the
asmcli help group-access
command.
Considerations for Thin-Provisioning
Several characteristics are considered when eqlvolume determines whether or not a volume can be thin-provisioned. See the following
sections for more information:
•
File System and Volume Characteristics
•
Multiple File Systems
File System and Volume Characteristics
The eqlvolume tool uses characteristics of the file system and the EqualLogic volume, as well as defined configuration parameters to
determine if a volume can be rethinned. For information on the defined configuration parameters, see
Volume Thin-Provisioning
Configuration Parameters
.
File system characteristics that prevent eqlvolume from recommending rethinning include:
•
Read-only file system—A file system that is mounted as read-only cannot be updated, nor can space be allocated or deallocated.
•
Lack of
FITRIM ioctl()
or
-o discard
support—Thin-provisioning requires either
FITRIM ioctl()
or
-o discard
support. If a file system was not mounted with the
-o discard
option, eqlvolume might need to remount that file system using the
-o discard
option, perform on-demand thin-provisioning, and remount the file system with the
-o nodiscard
option. A file
system that does not support
-o nodiscard
cannot be restored to its original state after thin-provisioning, and eqlvolume will not
recommend that file system for on-demand thin-provisioning.
•
A
gfs2
file system without FITRIM support—Thin-provisioning a
gfs2
file system by allocating most of the disk space and deleting
the temporary files is very slow, so eqlvolume does not recommend thin-provisioning a
gfs2
files system without FITRIM.
•
Insufficient free space—Without sufficient free space in the file system, eqlvolume is unlikely to recover any significant free space on
the volume.
EqualLogic volume characteristics that prevent eqlvolume from recommending thin-provisioning include:
•
Target is a snapshot—Snapshots only store changes to the volume, so they are already space efficient.
•
Volume is not t1in-provisioned—If the volume is not thin-provisioned, space is preallocated to the volume, and free space cannot be
recovered.
•
Firmware—Firmware in the PS Series group does not support unmaps, or discards.
•
Replication or synchronous replication is configured—Replicated volumes do not support thin-provisioning.
•
Volume is a replica failover volume—The product of a replicated volume is not a good candidate for thin-provisioning.
Multiple File Systems
If all of the characteristics of the file system and the volume indicate that on-demand thin-provisioning is possible, eqlvolume recommends
thin-provisioning based on a comparison of the space used by the file systems and the volumes that support them.
When eqlvolume evaluates multiple file systems built by multiple logical volumes from one or more target volumes or file systems built by
partitions, the function compares the total amount of space used by all of the related file systems to the total amount of space used by
the target volumes. If the space used by the target volumes is significantly greater than the space used by the file systems, all of the file
systems are recommended for thin-provisioning because it is impossible to predict what free space was originally part of which file system.
If a target volume supports multiple file systems through logical volumes or partitions, and one or more of those file systems are not
mounted, eqlvolume cannot include the amount of space used by the unmounted file systems. In this circumstance, eqlvolume will likely
recommend that the remaining file systems be thin-provisioned.
For example, if two partitions (file systems) each use 100GB, and the target volume has 300 GB of space in use, eqlvolume will
recommend that the two partitions be thin-provisioned. However, if a third partition is using 100 GB of space but is not mounted, the
space used by the third (unmounted) partition can cause eqlvolume to recommend thin-provisioning, although the thin-provisioning will
likely not recover any free space.
Managing Thin-Provisioned Volumes
99