RAID LUNs Test

A logical unit number (LUN) is a unique identifier used to designate individual or collections of hard disk devices for address by a protocol associated with a SCSI, iSCSI, Fibre Channel (FC) or similar interface. LUNs are central to the management of storage arrays shared over a storage area network (SAN). LUN errors, poor LUN cache usage, and abnormal I/O activity on the LUNs, if not promptly detected and resolved, can hence significantly degrade the performance of the storage array. This is why, it is important that LUN performance is continuously monitored. This can be achieved using the RAID LUNs test. This test auto-discovers the LUNs in the storage system and reports the current state of each LUN, captures LUN errors, and measures the level of I/O activity on every LUN, so that administrators are notified of LUN-related problems well before they impact storage system performance.

Target of the test : An SMI-S compliant storage device

Agent deploying the test : A remote agent

Outputs of the test : One set of results for each LUN on the storage system.

Configurable parameters for the test
Parameter Description

Test period

How often should the test be executed

Host

The IP address of the storage device.

Port

The port number at which the storage device listens to. By default, this is NULL.

User and Password

Specify the credentials of a user who has the right to execute API commands on the storage device and pull out metrics. The exact role that is to be assigned to such a user will differ from one device to another – for instance, when monitoring 3PAR, you will have to provide the credentials of a user who has been assigned the Monitor role, here. 

Confirm Password

Confirm the password by retyping it here.

SSL

Set this flag to Yes, if the storage device being monitored is SSL-enabled.

IsEmbedded

If this flag is set to True, it indicates that the SMI-S provider is embedded on the storage platform. On the other hand, if this flag is set to False, it indicates that the SMI-S provider has been implemented as a proxy.

SerialNumber

If the SMI-S provider has been implemented as a proxy, then such a provider can be configured to manage multiple storage devices. This is why, if the IsEmbedded flag is set to False, you will have to explicitly specify which storage system you want the eG agent to monitor. Since each storage system is uniquely identified by a SerialNumber, specify the same here. The format of this number and where you can find it will differ from one storage system to another. You are hence advised to contact the storage administrator to know what to enter against SerialNumber. For example, the serial number for an EMC CLARiiON device will be of the format, FCNMM094900059.

NameSpace

Specify the namespace that uniquely identifies the profiles specific to the provider in use.

Measurements made by the test
Measurement Description Measurement Unit Interpretation

Health state

Indicates how healthy this LUN currently is.

 

The values that this measure can report and their corresponding numeric values are discussed in the table below:

Numeric Value Measure Value
0 OK
1 Unknown
2 Degraded/Warning
3 Minor failure
4 Major failure
5 Critical failure
6 Non-recoverable error

Note:

By default, this measure reports the Measure Values discussed above to indicate the state of a LUN In the graph of this measure however, states are represented using the numeric equivalents only.

Operational status

Indicates the current operational state of this LUN.

 

The values that this measure can report and their corresponding numeric values are discussed in the table below:

Numeric Value Measure Value
0 OK
1 In Service
2 Power Mode
3 Completed
4 Starting
5 Dormant
6 Other
7 Unknown
8 Stopping
9 Stressed
10 Stopped
11 Supporting Entity in Error
12 Degraded or Predicted Failure
13 Predictive Failure
14 Lost Communication
15 No Contact
16 Aborted
17 Error
18 Non-Recoverable Error

Note:

By default, this measure reports the Measure Values discussed above to indicate the operational state of a LUN. In the graph of this measure however, operational states are represented using the numeric equivalents only.

Detailed operational state

Describes the current operational state of this LUN.

 

This measure will be reported only if the API provides a detailed operational state.

Typically, the detailed state will describe why the LUN is in a particular operational state. For instance, if the Operational status measure reports the value Stopping for a LUN, then this measure will explain why that LUN is being stopped.

The values that this measure can report and their corresponding numeric values are discussed in the table below:

Numeric Value Measure Value
0 Online
1 Success
2 Power Saving Mode
3 Write Protected
4 Write Disabled
5 Not Ready
6 Removed
7 Rebooting
8 Offline
9 Failure

Note:

By default, this measure reports the Measure Values discussed above to indicate the detailed operational state of a LUN. In the graph of this measure however, detailed operational states are represented using the numeric equivalents only.

Data transmitted

Indicates the rate at which data was transmitted by this LUN.

MB/Sec

 

IOPS

Indicates the rate at which I/O operations were performed on this LUN.

IOPS

Compare the value of this measure across LUNs to know which LUN handled the maximum number of I/O requests and which handled the least. If the gap between the two is very high, then it indicates serious irregularities in load-balancing across LUNs.

You may then want to take a look at the Reads and Writes measures to understand what to fine-tune – the load-balancing algorithm for read requests or that of the write requests.

Reads

Indicates the rate at which read operations were performed on this LUN.

Reads/Sec

Compare the value of this measure across LUNs to know which LUN handled the maximum number of read requests and which handled the least.

Writes

Indicates the rate at which write operations were performed on this LUN.

Writes/Sec

Compare the value of this measure across LUNs to know which LUN handled the maximum number of write requests and which handled the least.

Data reads

Indicates the rate at which data is read from this LUN.

MB/Sec

Compare the value of these measures across LUNs to identify the slowest LUN in terms of servicing read and write requests (respectively).

Data writes

Indicates the rate at which data is written to this LUN.

MB/Sec

LUN busy

Indicates the percentage of time this LUN was busy processing requests.

Percent

Compare the value of this measure across LUNs to know which LUN was the busiest and which LUN was not. If the gap between the two is very high, then it indicates serious irregularities in load-balancing across LUNs.

Average read size

Indicates the amount of data read from this LUN per I/O operation

MB/Op

Compare the value of these measures across LUNs to identify the slowest LUN in terms of servicing read and write requests (respectively).

Average write size

Indicates the amount of data written to this LUN per I/O operation.

MB/Op

Read hit

Indicates the percentage of read requests that were serviced by the cache of this LUN.

Percent

A high value is desired for this measure. A very low value is a cause for concern, as it indicates that cache usage is very poor; this in turn implies that direct LUN accesses, which are expensive operations, are high.

Write hit

Indicates the percentage of write requests that were serviced by the cache of this LUN.

Percent

A high value is desired for this measure. A very low value is a cause for concern, as it indicates that cache usage is very poor; this in turn implies that direct LUN accesses, which are expensive operations, are high.

Average response time

Indicates the time taken by this LUN to respond to I/O requests.

Microsecs

Ideally, this value should be low. If not, it implies that the LUN is slow.

Queue depth

Indicates the number of requests that are in queue for this LUN.

Number

A consistent increase in this value indicates a potential processing bottleneck with the LUN.