Volume options

Volume options:

While we create a volume we have three options: volume,file,none lets discuss each of them in detail.

Volume—A guarantee of “volume” ensures that the amount of space required by the FlexVol

volume is always available from its aggregate. This is the default setting for FlexVol volumes.

With the space guarantee set to “volume” the space is subtracted, or reserved, from the

aggregate’s available space at volume creation time. The space is reserved from the aggregate

regardless of whether it is actually used for data storage or not.

The example shown here shows the creation of a 20GB volume. The df commands showing the

space usage of the aggregate before and after the volume create command display how the

20GB is removed from the aggregate as soon as the volume is created, even though no data has

actually been written to the volume. In simple terms this is for the space reserved volumes

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

filer1> vol create flex0 aggr0 20g

Creation of volume ‘flex0′ with size 20g on hosting aggregate ‘aggr0′ has

completed.

filer1> df -g /vol/flex0

Filesystem total used avail capacity Mounted on

/vol/flex0/ 16GB 0GB 16GB 0% /vol/flex0/

/vol/flex0/.snapshot 4GB 0GB 4GB 0% /vol/flex0/.snapshot

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 20GB 65GB 23%

aggr0/.snapshot 4GB 0GB 4GB 0%

Since the space has already been reserved from the aggregate, write operations to the volume

will not cause more space from the aggregate to be used.

——————————————————————————————————————————————————————–

·None—A FlexVol volume with a guarantee of “none” reserves no space from the aggregate

during volume creation. Space is first taken from the aggregate when data is actually written to

the volume. The example here shows how, in contrast to the example above with the volume

guarantee, the volume creation does not reduce used space in the aggregate. Even LUN

creation, which by default has space reservation enabled, does not reserve space out of the

aggregate. Write operations to space-reserved LUNs in a volume with guarantee=none will fail if

the containing aggregate does not have enough available space. LUN reservation assure that

the LUN has space in the volume but guarantee=none doesn’t assure that the volume has space

in the aggregate. In simple terms this is for the thin provisioned volumes

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

filer1>

filer1> vol create noneflex -s none aggr0 20g

Creation of volume ‘noneflex’ with size 20g on hosting aggregate

‘aggr0′ has completed.

filer1>

filer1> df -g /vol/noneflex

Filesystem total used avail capacity Mounted on

/vol/noneflex/ 16GB 0GB 16GB 0% /vol/noneflex/

/vol/noneflex/.snapshot 4GB 0GB 4GB 0% /vol/noneflex/.snapshot

filer1>

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

filer1> lun create -s 10g -t windows /vol/noneflex/foo

Mon Oct22 18:17:28 IST [array1: lun.vdisk.spaceReservationNotHonored:notice]:

Space reservations in noneflex are not being honored, either because the volume

space guarantee is set to ‘none’ or the guarantee is currently disabled due to

lack of space in the aggregate.

lun create: created a LUN of size: 10.0g

filer1>

filer1> df -g /vol/noneflex

Filesystem total used avail capacity Mounted on

/vol/noneflex/ 16GB 10GB 6GB 0% /vol/noneflex/

/vol/noneflex/.snapshot 4GB 0GB 4GB 0% /vol/noneflex/.snapshot

filer1>

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

——————————————————————————————————————————————–

File—With guarantee=file the aggregate assures that space is always available for overwrites to

space-reserved LUNs( we make the lun as thick). Fractional reserve is

set to 100% and is not adjustable with this type of guarantee. The “file” guarantee is basically the

same as the “none” guarantee with the exception that space reservations for LUNs and spacereserved

files are honored. The example below looks the same as the previous example under

with guarantee=none except in this example the LUN creation takes space from the aggregate

because it is a space-reserved object. Since the space reservation is honored, the “lun create”

command also doesn’t issue the warning shown in the previous example. This is for the thick provisioned luns

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

filer1>

filer1> vol create noneflex -s file aggr0 20g

Creation of volume ‘noneflex’ with size 20g on hosting aggregate

‘aggr0′ has completed.

cnrl1>

filer1> df -g /vol/noneflex

Filesystem total used avail capacity Mounted on

/vol/noneflex/ 16GB 0GB 16GB 0 % /vol/noneflex/

/vol/noneflex/.snapshot 4GB 0GB 4GB 0%

/vol/noneflex/.snapshot

filer1>

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 0GB 85GB 0%

aggr0/.snapshot 4GB 0GB 4GB 0%

filer1>

filer1> lun create -s 10g -t windows /vol/noneflex/foo

lun create: created a LUN of size: 10.0g

filer1>

filer1> df -g /vol/noneflex

Filesystem total used avail capacity Mounted on

/vol/noneflex/ 16GB 10GB 6GB 0% /vol/noneflex/

/vol/noneflex/.snapshot 4GB 0GB 4GB 0% /vol/noneflex/.snapshot

filer1>

filer1> df -A -g aggr0

Aggregate total used avail capacity

aggr0 85GB 10GB 75GB 12%

aggr0/.snapshot 4GB 0GB 4GB 0%