Configuring Eseutil throttling for database verification

When installed with Exchange 2003 SP2, SnapManager supports the ability to throttle the database checksum verification rate. For more information, see the following topics:

About database verification load

Database verification can place a significant load on both the Exchange server and the storage system. For this reason, verification can degrade Exchange Server response, particularly during peak work hours. With SnapManager 3.1 and earlier releases, there are two options for distributing this load by separating database verification database backup operations: deferred database verification and remote database verification.

SnapManager 3.2 supports a third option for managing database verification, that you can combine with either or both of the existing options, to reduce the load even further. When installed with Microsoft Exchange 2003 SP2, SnapManager 3.2 supports the ability to throttle Eseutil (the Microsoft Exchange consistency checker utility) in database checksum verification mode.

Requirements for using the Eseutil throttling option

This Eseutil throttling feature was first introduced with Exchange 2003 SP2, and SnapManager 3.2 provides a configuration option for configuring this feature.

Note
Attempting to use the throttling feature with earlier versions of SnapManager or Exchange will have no effect.

How the database verification throttling feature works

Exchange 2003 SP2 added a feature to Eseutil.exe, the Microsoft Exchange consistency checker utility, that can insert a one-second pause after a given number of I/O operations during the database physical consistency verification.

The effect of using different throttling values

Eseutil.exe reads 512 KB for each database checksum verification I/O operation. Therefore, when configuring the throttling value, the maximum throughput rate for database checksum verification is decreased to the following:

512 KB per I/O × x I/Os per second = 512 × x KB/second

To decrease the maximum throughput rate, decrease the number of I/O operations (x) that elapse between one-second pauses. The following examples illustrate the effect of using throttling values of 100, 150, 200, and 250 for x.

Number of I/O operations (x) between one-second pauses

Maximum possible database verification speed

Calculation

Maximum

speed

100

512 KB/IO × 100 IO/sec = 51,200 KB/sec

50 MB/sec

150

512 KB/IO × 150 IO/sec = 76,800 KB/sec

75 MB/sec

200

512 KB/IO × 100 IO/sec = 102,400 KB/sec

100 MB/sec

250

512 KB/IO × 250 IO/sec = 128,000 KB/sec

125 MB sec

Number of I/O operations (x) between one-second pauses	Maximum possible database verification speed
Calculation	Maximum speed
100	512 KB/IO × 100 IO/sec = 51,200 KB/sec	50 MB/sec
150	512 KB/IO × 150 IO/sec = 76,800 KB/sec	75 MB/sec
200	512 KB/IO × 100 IO/sec = 102,400 KB/sec	100 MB/sec
250	512 KB/IO × 250 IO/sec = 128,000 KB/sec	125 MB sec

Note
Decreasing the Eseutil.exe database verification throughput causes the database checksum verification to take longer to complete. This also means that a backup job that is configured with verification will also take longer to complete. However, decreasing verification throughput does not cause a backup job without verification configured to take any longer to complete.

Choosing the sleep interval

Calculate the appropriate sleep interval value to use for each Exchange server. This entails monitoring the read and write performance of the LUNs on which the Exchange databases reside and then adjusting the verification throttle setting so that the average and peak physical disk performance is below the maximum values determined by Microsoft.

To calculate the Eseutil throttling value for a specific Exchange server, complete the following steps.

Step	Action
1	Launch the Windows Performance Monitor utility (also known as "Perfmon") on the machine that is the Exchange server.
2	Add the following Perfmon counters for each Data ONTAP LUN that contains an Exchange database: PhysicalDisk\Average Disk sec/Read PhysicalDisk\Average Disk sec/Write Note Monitor the LUNs containing the live Exchange databases, not the LUN in Snapshot copy that is mounted and verified by the verification process.
3	Monitor these pairs of values while a SnapManager verification job or a backup job with verification is in progress. Follow these guidelines: To monitor the SnapManager progress, watch the Backup Status window that is displayed during a manually launched backup job. If monitoring a backup with verification job, be sure to monitor the counters during the verification portion of the job. Multiple databases on the same Exchange server are verified sequentially, so be sure to monitor the counters for all of the database verifications. Monitor the counters during the busiest time of day that a verification or backup with verification job might occur.
4	The throttle setting is global, so select the reading from the database that exhibits the worst performance (highest readings).
5	Compare the measured values to the maximum values recommended by Microsoft. PhysicalDisk\Average Disk sec/Read The average physical disk performance times determined by Microsoft are as follows: Average read time should be below 20 ms. Maximum peak read time should be below 50 ms. PhysicalDisk\Average Disk sec/Write The maximum physical disk performance times determined by Microsoft are as follows: Average write time should be below 20 ms. Maximum peak write time should be below 50 ms. Note These values are good guidelines during peak Exchange usage hours. During off-peak Exchange hours, higher latencies may be acceptable.
6	If the measured values exceed the maximum values recommended by Microsoft, adjust the throttle setting to decrease the verification throughput rate.

Configuring the throttling option

To configure database verification throttling, complete the following steps on every Windows host system that will be performing database verification and is running Exchange 2003 SP2.

Note
You can configure the throttling option on all systems involving database verification, but the throttling feature of Eseutil is only supported by Exchange 2003 SP2.

Step

Action

1
Open the Verification Settings dialog box.

From the...

Do this...

SnapManager menu bar

Select Options > Database Verification Settings.

Backup Wizard

Go to the Verify the Databases and Transaction Logs in this Backup screen, and then click Verification Settings.

Restore Wizard

Go to the Verify Database Integrity in the Selected Backup screen (displayed only if you choose to restore from an unverified backup, and then click Verification Settings.

2
Select the Eseutil Throttling tab.

3
Select or deselect the "Throttle Eseutil database checksum verification" option to enable or disable the Eseutil throttling feature.

Note
The "Throttle Eseutil database checksum verification" option is accessible only if the verification server is installed with Microsoft Exchange 2003 SP2.
Result

If you enabled the Eseutil throttling feature, the "Pause for 1 second after x I/O operations" box displays the current sleep interval. The default value is 150. If you disabled the feature, the box is grayed out and inaccessible.

4
If you enabled the Eseutil throttling feature, enter a positive integer value in the "Pause for 1 second after x I/O operations" box. The default value is 150.

Enter the number I/O operations to complete before pausing for one-second during the database physical consistency check.

Refer to the formula and example calculations in The effect of using different throttling values. It has been observed that using a value in the range of 100 to 250 is suitable for most environments.

5
Click OK.

Step	Action
1	Open the Verification Settings dialog box.
From the...	Do this...
SnapManager menu bar	Select Options > Database Verification Settings.
Backup Wizard	Go to the Verify the Databases and Transaction Logs in this Backup screen, and then click Verification Settings.
Restore Wizard	Go to the Verify Database Integrity in the Selected Backup screen (displayed only if you choose to restore from an unverified backup, and then click Verification Settings.
2	Select the Eseutil Throttling tab.
3	Select or deselect the "Throttle Eseutil database checksum verification" option to enable or disable the Eseutil throttling feature. Note The "Throttle Eseutil database checksum verification" option is accessible only if the verification server is installed with Microsoft Exchange 2003 SP2. Result If you enabled the Eseutil throttling feature, the "Pause for 1 second after x I/O operations" box displays the current sleep interval. The default value is 150. If you disabled the feature, the box is grayed out and inaccessible.
4	If you enabled the Eseutil throttling feature, enter a positive integer value in the "Pause for 1 second after x I/O operations" box. The default value is 150. Enter the number I/O operations to complete before pausing for one-second during the database physical consistency check. Refer to the formula and example calculations in The effect of using different throttling values. It has been observed that using a value in the range of 100 to 250 is suitable for most environments.
5	Click OK.

Entries in the SnapManager backup and verification report

Before each database verification, the SnapManager backup and verification report indicates whether the feature is enabled:

If the feature is enabled, the report includes the following entry:
ESEUTIL throttling feature is enabled.
If the feature is not enabled, the report includes the following entries:
ESEUTIL throttling feature is disabled.

ESEUTIL output will show the throttling parameter.

Configuring Eseutil throttling for database verification

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