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Oversights such as inadequate storage capacity, poor storage resilience, careless disk selection, overlooked storage options and even misunderstood server computing resources can wreak havoc on an Exchange deployment.
Microsoft Exchange 2013 is heavily dependent on storage. The mailbox server and supplemental tasks, such as content indexing and log retention, cannot perform to spec without the right storage options and setup.
Overcome Exchange 2013 storage sizing issues
Properly sizing the Exchange 2013 infrastructure before deploying it ensures optimum performance at launch and allows for reasonable growth into the foreseeable future without unnecessary waste. Every mailbox uses storage, transaction logs and content indexes, so adequate storage capacity is crucial.
A tool for the job
Although it's possible to manually estimate Exchange 2013 storage requirements, comprehensive storage capacity planning can be simplified using the Exchange 2013 Server Role Requirements Calculator. Microsoft TechNet offers Version 6.6 of this calculator, which can gather infrastructure characteristics and produce detailed results. Administrators can use the tool to quickly gauge what-if scenarios and check the effects of the overall Exchange storage deployment growth.
User profiles. Proper sizing starts with an assessment of user profile needs -- the total storage of average messages sent and receives per user, per day. The storage may need to be divided between user groups because message numbers can vary. Suppose the average end user exchanged 300 messages per day at 100 KB per message. This would comprise about 30 MB of daily usage, or white space storage.
Recoverable items. Figure the folder size for all recoverable items that receive deleted emails until their retention period expires, allowing for email recovery. Estimate the size by multiplying the number of messages per day times the average message size times the retention window; that is, a 420 MB retention window for a two-week period. Add to this another 4.2% of the mailbox quota size for calendar and other content. For example, if the mailbox quota is set to 12 GB, this would add 504 MB for recoverable items. Thus the total mailbox size would be 12 GB of quota plus the daily usage plus the recoverable items folder, or about 12.534 GB per mailbox.
Content indexing. Content indexing takes up about 20% of the mailbox database size on the storage volume -- plus one additional database set aside for maintenance tasks. So, if you have one 300 GB mailbox database on the volume, allocate 120 GB. If you have two 180 GB mailbox databases on the volume, allocate 108 GB.
Log files. Each log file is 1 MB, so to allocate storage, gauge the number of log files produced per day. The number of log files is roughly 20% of the number of 75 KB messages: If you exchange about 300 messages per day at 75 KB per message, Exchange produces about 60 log files, or 60 MB of log file storage. Every time the message size doubles, the log files increase by a factor of about 1.9, so the same 300 messages per day at 150 KB per message would be about 114 log files or 114 MB. And with 300 KB messages, the same 300 emails would generate about 228 log files or 228 MB of log file storage.
Additional considerations include the log space needed to support mailbox moves and support for failed logs. Investigate sizing tool calculators to estimate log storage. These calculators accommodate a number of situations beyond simple storage -- log storage can easily involve 10 to 20 GB or more depending on the demands.
These examples give you a taste of Exchange 2013 storage sizing, but take the evaluation a step further. Storage input/output operations per second (IOPS) vary based on the number of end users per mailbox database and the messages exchanged per day. Storage bandwidth is typically recommended at 1 MB per second per database copy for background database maintenance, which can be a limiting issue in some disk subsystems. You'll need additional transport storage to queue messages and this storage is dependent on bandwidth and IOPS requirements.
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