Network Appliance NS0-093 Practice Test - Questions Answers, Page 3

In a SAS stack of shelves, the connection between the expander and the disk uses a point-to-point topology.

Key Details:

Point-to-Point:

Each SAS disk in a shelf connects directly to the expander using a dedicated channel. This ensures that communication between the disk and expander is independent of other disks, improving performance and reliability.

Why SAS Uses Point-to-Point:

SAS (Serial Attached SCSI) eliminates the shared bandwidth limitations of traditional bus architectures (e.g., arbitrated loop or ring) by dedicating a connection to each device.

Why Other Options Are Incorrect:

A . arbitrated loop:

Arbitrated loop is a topology used in Fibre Channel systems, not SAS.

C . loop:

SAS does not use loop-based communication; this is typical of older technologies like SCSI Parallel Interface (SPI).

D . ring:

Ring topology is not used in SAS stacks.

'NetApp SAS Shelf and Disk Configuration Guide' specifies point-to-point communication between expanders and disks in SAS environments.

1. L1 Watchdog Reset (WDR):

Description:

L1 WDR is a hardware-initiated reset that occurs when the system detects an unrecoverable error or lockup lasting 0.5 seconds.

Key Characteristics:

It performs a hard reset, meaning the system immediately reboots without creating a core dump.

2. L2 Watchdog Reset (WDR):

Description:

L2 WDR is initiated when the system fails to recover from a critical fault after 2 seconds.

Key Characteristics:

It requests a core dump to capture the system state for diagnostic purposes before performing a reset.

Why Other Options Are Incorrect:

B . L1 WDR is initiated after 0.5 seconds from the event:

This is incorrect because L1 WDR performs a hard reset and does not initiate after 2 seconds.

C . L1 WDR performs a soft reset:

This is incorrect because L1 WDR performs a hard reset, not a soft reset.

'ONTAP Panic Analysis Guide' describes the behavior and timing of L1 and L2 WDR events.

NetApp Support documentation on system resets explains the differences between L1 and L2 watchdog resets.

To reset environment variables to factory settings, the set-defaults command is used. This command clears all customizations and restores the environment variables to their default values.

Key Details:

Command Syntax: At the LOADER prompt, type:

arduino

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set-defaults

Effect: This command resets all environment variables (e.g., boot arguments, diagnostic settings) to their original factory defaults.

Why Other Options Are Incorrect:

B . unsetenv all:

This command clears all environment variables, but it does not restore them to factory defaults.

C . setenv factory:

This is not a valid command in NetApp systems.

D . wipeconfig:

This command is used to clear configuration and logs but does not reset environment variables.

NetApp 'System Configuration Guide' confirms the use of set-defaults for restoring environment variables to factory settings.

Write Acknowledgment in NetApp ONTAP:

In a clustered ONTAP system, write requests are acknowledged to the client only after they are securely stored in NVRAM on both the local node and its HA (High Availability) partner.

This ensures redundancy and data protection in case of a node failure.

Why Other Options Are Incorrect:

A . when the write is present in the local node RAM and NVRAM:

Writes are not acknowledged until the HA partner also stores the data in its NVRAM.

B . when the write has been flushed to disk:

Writes are acknowledged before they are written to disk, as NVRAM ensures durability.

D . when the write has been flushed from NVRAM to RAM:

Data is not acknowledged based on RAM; NVRAM on both nodes is the requirement.

NetApp's 'ONTAP Write I/O Processing Guide' explains the role of NVRAM and HA in write acknowledgment.

'Data Protection in ONTAP' highlights the synchronization of NVRAM between HA partners.

Purpose of the diskcopy Command:

The diskcopy command is used in the ONTAP nodeshell environment to perform a low-level sector-by-sector copy of data from one disk to another. This is typically used during data recovery or diagnostics.

How It Works:

The command copies all sectors from the source disk to the destination disk without any regard for file system or metadata structures.

It is commonly used when replicating the exact state of a failing disk to a spare for further analysis or recovery.

Key Notes:

The destination disk must be of the same or larger capacity than the source disk.

The operation is typically disruptive and not suitable for production use.

NetApp Reference Documentation:

Found in the 'ONTAP Command Line Manual' for nodeshell utilities. The diskcopy process is highlighted as a low-level disk cloning operation.

Reverting to a Previous ONTAP Version:

Reverting ONTAP software requires specific procedures and is only supported if the ONTAP version being reverted to is compatible with the current cluster configuration.

Why the Netboot Procedure Is Used:

The netboot process loads the desired ONTAP version directly into memory from a network location and reinitializes the system.

This method is used when a full software revert is required and is often necessary for downgrades to a version that cannot be directly reverted to from the running ONTAP version.

Key Notes:

A direct revert is not supported from ONTAP 9.7 to ONTAP 9.5 using standard methods due to system metadata changes.

Always verify compatibility using the 'ONTAP Software Version Interoperability Matrix'.

NetApp Reference Documentation:

Refer to the 'ONTAP Revert/Downgrade Guide' for specific instructions on using the netboot procedure.

Steps to Unfail a Disk in Maintenance Mode:

When a disk is marked as 'failed,' it is added to the Failed Disk Registry and marked as unusable by the system. Unfailing a disk involves removing it from this registry and resetting its state.

Step 1: Remove the Disk from the Failed Disk Registry

Use the command: registry remove <disk> to delete the disk from the Failed Disk Registry. This clears its 'failed' status.

Step 2: Use the Disk Unfail Command

Execute the disk unfail <disk> command to reset the disk status and make it available for use.

Key Notes:

After unfailing, the disk will be treated as a spare and must be reassigned or re-added to an aggregate.

If the disk remains failed after these steps, physical hardware issues may need to be addressed.

NetApp Reference Documentation:

The 'ONTAP Maintenance Mode Guide' and 'Disk Management Guide' provide detailed instructions for handling failed disks and using the disk unfail command.

Understanding a Single PHY Down Issue:

In SAS environments, a PHY represents a physical layer connection between devices.

When a single PHY reports a 'down' status, it typically indicates an issue with the physical connectivity or the associated hardware.

Cause 1: Improperly Seated Cable

If the SAS cable is not properly seated in the port, the connection for one or more PHYs may fail.

Reseating the cable on both ends (controller and shelf) often resolves the issue.

Cause 2: Defective Cable

A damaged or faulty SAS cable can cause PHY errors.

Replacing the cable and verifying the connection resolves the issue in this case.

Why Other Options Are Not Likely:

B . Outdated IOM firmware: While outdated firmware can cause other issues, it rarely affects only a single PHY.

D . Offline shelf: If an entire shelf is offline, more than one PHY would typically be affected, as multiple connections are involved in SAS stacks.

NetApp Reference Documentation:

Found in the 'ONTAP SAS Cabling Guide' and 'Shelf Troubleshooting Guide'. These documents detail troubleshooting for PHY errors and common SAS hardware issues.

When an aggregate fails due to multiple disk failures caused by a faulty I/O module (IOM), the first step after replacing the faulty IOM is to manually unfail the affected drives. This process is done in maintenance mode.

Steps to Recover the Aggregate:

Enter Maintenance Mode:

Reboot the node and interrupt the boot process to access maintenance mode.

Identify Failed Drives:

Use the command:

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storage show disk --broken

This command lists all failed (broken) drives.

Unfail the Drives:

Use the following command for each failed drive:

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disk unfail <disk-name>

Reconstruct the Aggregate:

Once all drives are unfail, the system should begin reconstructing the RAID groups in the aggregate.

Why Other Options Are Incorrect:

A . Use diskcopy from maintenance mode:

Diskcopy is used for cloning or copying data between disks, not for recovering failed aggregates.

B . Run wafliron from the boot_menu:

wafliron is used to repair WAFL inconsistencies, but it does not help recover failed aggregates due to disk issues.

D . Unfail the drives in the order that they failed from the clustershell:

Drives must be unfail in maintenance mode, not from the clustershell.

NetApp's 'Aggregate and RAID Troubleshooting Guide' explains the process of recovering aggregates and using maintenance mode commands.

'ONTAP Disk Recovery Guide' outlines steps to unfail disks and recover RAID groups.