Basics Currency Trading Ru Here Service Basic Currency Trading Best Practices for Configuring Exchange Back-End Storage

This section provides information to help you properly configure the location and RAID levels for the following types of Exchange data:

• Database files (.edb and .stm files)
  
• Transaction log files
  
• SMTP Queue directory data
  
• Content indexing files
  

An Exchange database consists of a rich-text .edb file and a Multipurpose Internet Mail Extensions (MIME) content .stm file.

The .edb file stores the following items:

• All of the MAPI messages
  
• Tables used by the Store.exe process to locate all messages
  
• Checksums of both the .edb and .stm files
  
• Pointers to the data in the .stm file
  

The .stm file contains messages that are transmitted with their native Internet content. Because access to these files is generally random, they can be placed on the same disk.

By default, Exchange stores database files in the following folder:

drive:\Program Files\Exchsrvr\MDBDATA

This folder exists in the same partition on which you install Exchange 2003.

As you plan your storage solution for these files, implement a solution that ensures reliability. RAID-0 is not a recommended option. After reliability, your storage solution is based on a choice between optimizing performance (RAID-1) and optimizing capacity (RAID-5). If possible, use RAID-1 (or RAID-0+1) for these files.

You can store public folders on a RAID-5 array because data in public folders is usually written once and read many times. RAID-5 provides improved read performance.

The most important aspect of a storage group is its transaction logs. Even if you use only the default First Storage Group, you need to consider your transaction log configuration to be sure that you can recover data if the stores are damaged.

In standard Exchange transaction logging, each store transaction (such as creating or modifying a message) in a storage group is written to a log file and then to the Exchange store. All of the stores in a storage group share a single set of transaction logs. The logging process ensures that records of transactions exist if a store is damaged between backups. In many cases, recovering a damaged store means restoring the store from a backup, replaying any backed up log files, and then replaying the most recent log files to recover transactions that were made after the last backup.

If a disaster occurs, and you must rebuild a server, you use the latest transaction log files to recover your databases. If you have access to the latest backup and the transaction log files since the backup, you can recover all of your data. However, if you lose any of the transaction log files, the data that was not committed to the database since the last backup is permanently lost.

By default, Exchange stores transaction log files in the following folder:

drive:\Program Files\Exchsrvr\MDBDATA

This folder exists in the same partition on which you install Exchange 2003.

As you plan the location of your Exchange transaction log files, consider the following:

• You can significantly improve the performance and fault tolerance of Exchange servers by placing each set of transaction log files on a separate drive.
  
• Because each storage group has its own set of transaction log files, the number of dedicated transaction log drives for your server should equal the number of planned storage groups. With a SAN solution, you can select a product to easily partition the virtualized space into separate virtual drives for storage groups and transaction log files.
  
• In addition, because transaction log files are critical to the operation of a server, you should protect the drives against failure, ideally by hardware mirroring using RAID. A RAID-0+1 configuration (in which data is mirrored and then striped) is recommended.
  

An example disk configuration is as follows:

• C:\ System and boot (mirror set)
  
• D:\ Page file
  
• E:\ Transaction log files for storage group 1 (mirror set)
  
• F:\ Transaction log files for storage group 2 (mirror set)
  
• G:\ Database files for both storage groups (multiple drives configured as hardware stripe set with parity
  

• System partition
  
• Partition containing Exchange binaries
  
• Partitions containing transaction log files
  
• Partitions containing database files
  
• Partitions containing other Exchange files
  

The SMTP Queue directory has an important role in the Simple Mail Transfer Protocol (SMTP) message queuing process. The SMTP Queue directory stores SMTP messages until they are written to a database (public or private, depending on the type of message) or sent to another server or connector. Because the SMTP queuing process is write-intensive, it is important to configure your system for maximum performance.

Typically, messages are stored in the SMTP queue for a short time. However, in some situations (particularly when downstream processes fail), the SMTP queue could be required to store a large amount of data. Therefore, your storage solution for the SMTP queue should optimize performance before considering capacity and reliability.

By default, Exchange stores SMTP messages in the following folder:

drive:\Program Files\Exchsrvr\Mailroot

This folder exists in the same partition on which you install Exchange 2003. In some scenarios (for example, when you configure a bridgehead server), you can improve the performance of the Exchange 2003 server if you move the Mailroot folder to a different hard disk or partition.

As you plan the location of your SMTP queue data, consider the following:

• Do not assume that a RAID-0 array is the best storage solution for SMTP queues. Generally, RAID-0 is acceptable only if mail loss is acceptable. RAID-1 is a good solution because it gives some measure of reliability while providing adequate throughput. However, if you are looking for the highest performance and reliability, using RAID-0+1 for the SMTP queue is worth the extra investment.
  
• In Exchange 2003, you can now use Exchange System Manager to change the location of the Queue directory. In Exchange System Manager, this option is available from the Message tab of the SMTP virtual server object.
  

Content indexing causes excessive paging while the databases are being scanned, as well as excessive writes to the content indexing file. As a result, the content indexing file should not be located on the same disk as the page file (although that is the default location). Because the content indexing file is a random-access file, it can be placed on the same drive as the databases, provided that the disk subsystem can handle the load.

Ensure that you have adequate hard disk capacity for your Exchange servers. You should have enough space on your hard disk to restore both the database and the log files.

You could have a backup that is too large to restore to its original location. For example, a normal backup performed once a week, plus six days of differential backups, might require more disk space during a restore than your server has available. Whether the restore requires more disk space than you have available depends on how many log files are generated during a week. For example, a server generating 2,000 log files in a week amounts to 10 GB of log file space, in addition to the space required for the database.

Performing normal backups on a daily basis reduces the amount of space required to restore your Exchange databases. The reason for this reduced space is that normal backups delete the transaction log files up to the time that you perform the backup. If you need to restore your Exchange databases, perform normal backups on a daily basis to ensure that you do not have to restore more than one day's worth of log files.

Also, you should never let your database drive (the hard disk containing the .edb and .stm files) become more than half full. Although a database drive that is half full results in unused disk space, it can still reduce extended server downtime for the following reasons:

• You can restore databases faster than with a full drive (especially if the file system is fragmented).
  
• You can perform offline defragmentation on the same physical disk instead of copying databases over to a maintenance server (a task that takes much longer than copying database files to a temporary directory on the same physical hard disk).
  
• You can back up a copy of the databases to the same physical disk before you restore them, which enables you to attempt to repair the databases if a problem occurs during the restore process (for example, if the existing backup contains errors). For this reason, it is recommended that you move or copy the current database and log files before restoring a database. For information about restoring Exchange databases, see the Exchange Server 2003 Disaster Recovery Operations Guide.
  

  Примечание.
  Given the large size of the average database, copying your most current database to a different physical disk drive or to another server may add several hours to your downtime. However, if you have sufficient local disk space on the same physical drive, you can move the current database files to another folder by using a command prompt or Windows Explorer before you perform the restore.

Having sufficient disk I/O throughput to support a specific number of users is just as important as having sufficient disk space. This is especially important for disk-intensive applications such as Exchange 2003. In general, the speed and number of physical disks have the largest influence on the overall storage system performance. If large or slow disks are used on a SAN to provide the required storage space, disk I/O requirements (and not storage space) become the deciding factor for sizing the storage configuration. In such a case, more disks may be required, not for the additional storage space, but for the increased I/O provided by the additional spindles.

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