3Ware 9550SXU-16ML User Guide - Page 131

Disabling Write Cache on Unit Degrade, Multi LUN Support and Auto-Carving, Policy, Enter, Degrade

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Viewing and Setting Controller Policies Disabling Write Cache on Unit Degrade Note: This procedure applies only to 9500S controllers. For 9550SX controllers, this feature is integrated into the StorSave Profile. You can choose whether you want the write cache to be automatically disabled when a unit degrades. This enables some higher level recovery, to cover the case where there is a software RAID layer (using some redundancy) on top of the 3ware RAID configuration. In case of a second drive failure, the software RAID layer can still provide redundancy since no data was lost. When this setting is set to Yes, it overrides the write cache setting specified for a particular unit. You can change this setting in 3BM or using the CLI. For more information about enabling and disabling the write cache, see"Enabling and Disabling the Unit Write Cache" on page 137. To disable write cache when a unit degrades 1 At the main 3BM screen, Tab to Policy and press Enter. 2 On the Policy Control screen, Tab to Disable Write Cache on Unit Degrade. 3 Press Enter to display the choices, use the arrow keys to select Yes, and press Enter again to select it. 4 Tab to the OK button and press Enter. You will notice a short delay as 3BM makes the policy changes. Multi LUN Support and Auto-Carving When the Auto-Carving policy is on, any unit larger than a specified size (known as the carvesize) is created as multiple chunks that can be addressed by the operating system as separate volumes. These chunks are sometimes known as multiple LUNs (logical units). However, throughout the 3ware documentation, they are referred to as volumes. Each volume can be treated as an individual disk with its own file system. The default carvesize is 2 TB; this size can be changed through the CLI. 3ware firmware supports a maximum of 8 volumes per controller, up to a total of 16 TB. If you are migrating a unit to a size that is larger than the carvesize and autocarving is on, multiple volumes will be created. Note: Using auto-carving can have an impact on performance. www.3ware.com 121

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Viewing and Setting Controller Policies
www.3ware.com
121
Disabling Write Cache on Unit Degrade
Note:
This procedure applies only to 9500S controllers. For
9550SX controllers, this feature is integrated into the StorSave
Profile.
You can choose whether you want the write cache to be automatically
disabled when a unit degrades. This enables some higher level recovery, to
cover the case where there is a software RAID layer (using some redundancy)
on top of the 3ware RAID configuration. In case of a second drive failure, the
software RAID layer can still provide redundancy since no data was lost.
When this setting is set to
Yes,
it overrides the write cache setting specified
for a particular unit. You can change this setting in 3BM or using the CLI.
For more information about enabling and disabling the write cache,
see“Enabling and Disabling the Unit Write Cache” on page 137.
To disable write cache when a unit degrades
1
At the main 3BM screen,
Tab
to
Policy
and press
Enter
.
2
On the Policy Control screen,
Tab
to
Disable Write Cache on Unit
Degrade
.
3
Press
Enter
to display the choices, use the
arrow keys
to select
Yes
, and
press
Enter
again to select it.
4
Tab
to the
OK
button and press
Enter
.
You will notice a short delay as 3BM makes the policy changes.
Multi LUN Support and Auto-Carving
When the Auto-Carving policy is on, any unit larger than a specified size
(known as the
carvesize
) is created as multiple chunks that can be addressed
by the operating system as separate volumes. These chunks are sometimes
known as multiple LUNs (logical units). However, throughout the 3ware
documentation, they are referred to as
volumes
. Each volume can be treated as
an individual disk with its own file system. The default carvesize is 2 TB; this
size can be changed through the CLI. 3ware firmware supports a maximum of
8 volumes per controller, up to a total of 16 TB.
If you are migrating a unit to a size that is larger than the carvesize and auto-
carving is on, multiple volumes will be created.
Note:
Using auto-carving can have an impact on performance.