Hardware manual

Group Administration Advanced volume operations
10–2
– For a volume with a reported size that is less than 100GB, when free volume reserve falls below 6% of the
reported volume size, the group allocates an additional 10% of the reported volume size.
Event messages inform you when in-use volume reserve surpasses a user
-defined limit and reaches the
maximum.
Thin provisioning space settings
Three settings control how the group allocates space to thin-provisioned volumes and when the group generates
events related to space usage:
• Minimum volume reserve – Mini
mum amount of pool space that the group allocates to the volume, based on
a percentage of the reported volume size. The default group-wide setting is 10%.
• In-use space warning limit – Amount of in-use
volume reserve that results in notification, based on a
percentage of the reported volume size. The default group-wide setting is 60%.
When in-use volume reserve reaches the in-use warning limit, the
group generates a warning event message.
Additional warning event messages occur as follows:
– For volumes larger than 200 GB, when the in-use volume reserve inc
reases by every additional 10 GB.
– For volumes smaller than 200 GB, when the in-use volume reserve increases by every additional 5%.
For example, if you create a thin-provisioned
volume with a size of 500 GB and set the warning limit to 75%, a
warning occurs when the amount of in-use volume reserve is more than or equal to 75% of 500 GB, or 375 GB.
• Maximum in-use
space – Maximum amount of in-use volume reserve (maximum size of the volume reserve),
based on a percentage of the reported volume size. The default group-wide setting is 100%.
The maximum in-use space value determines th
e behavior when the volume reserve reaches its maximum size:
– If the maximum in-use space value is less than 100%, and an initiator write exceeds this limit, the
write
fails. The group sets the volume offline and generates event messages.
If you increase the maximum in-use space value or the reported volume size (both operations require free
pool spac
e), the group automatically sets the volume online and writes succeed.
– If the maximum in-use space value is 100%, and an initiator writ
e exceeds this limit, the volume is not set
offline; However, the write fails, and the group generates event messages. If you increase the reported size
of the volume, writes succeed.
This behavior is the same as when in-use space for a volume that is not thin-provisioned reac
hes its
reported size.
The maximum in-use space value helps prevent one
volume from consuming all the pool free space and setting
other thin-provisioned volumes offline.
You can change the group-wide default volume settings (see Modifying group-wide volume settings on
page 9-5),
override the default values when you create a
thin-provisioned volume, or modify a volume and change the
settings.