Red Hat NETSCAPE ENTREPRISE SERVER 6.0 - ADMINISTRATOR Specifications download pdf (Page 129)

Estimating Snapshot Pool Requirements

Chapter 7 Snapshots 113

Snapshots and iSCSI Disks

Running a GuardianOS snapshot on a volume containing an iSCSI Disk will

abruptly disconnect any clients attempting to write to the iSCSI Disk and the

resulting snapshot may contain inconsistent data. Do not use GuardianOS

snapshots on a volume containing an iSCSI Disk.

To create a native snapshot of an iSCSI disk on Windows systems, use the VSS

feature described in “Configuring VSS/VDS for iSCSI Disks” on page 93.

Estimating Snapshot Pool Requirements

Snapshot data grow dynamically for as long as a snapshot is active and as long as

there is enough space available in the snapshot pool to store them. When the

snapshot pool approaches its capacity (at about 95 percent), the SnapServer deletes

the oldest snapshot’s data to create space for more recent snapshot data.

The default configuration allocates 80 percent of RAID capacity to the volume and

20 percent to the snapshot pool. You can adjust the size of the pool up (assuming

unallocated space exists) or down according to your needs. If you find that your

snapshot strategy does not require all of the space allocated to the snapshot pool by

default, consider decreasing snapshot pool capacity and reallocating the capacity to

the file system. To adjust the size of the snapshot pool, navigate to the

Storage >

Snapshots

screen, click the Snapshot Space button, then click the Raid Set for the

snapshot pool you want to adjust.

The number of snapshots that a RAID can support is a function of these factors:

• The space reserved for the snapshot data

• The duration of the snapshots you create

• The amount and type of write activity to the volume(s) since the snapshot was

created

The following table describes minimum and maximum allocation cases.

Allocate about 10% of RAID if Allocate about 25% of RAID if

• Activity is write-light

• Write access patterns are concentrated in

a few places

• A small number of Snapshots must be

available at any point in time

• Activity is write-heavy

• Write access patterns are randomized

across the volume

• A large number of Snapshots must be

available at any point in time

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Red Hat NETSCAPE ENTREPRISE SERVER 6.0 - ADMINISTRATOR Specifications Page 129