Autotuned_reserved_space is a new feature on the ZDLRA that you should be using

 Autotuned_reserved_space is a new policy setting that got released with 21.1 and you should be using it. When I talk to customers about how to manage databases on a ZDLRA, the biggest confusion comes in when I talk about reserved space.  Reserved space needs to be understood, and properly managed. This new feature in 21.1 allows the ZDLRA to handle the reserved space for you, and I explain how to use it in this blog post.  First let's go through space usage, and reserved space in general.

Space usage on the ZDLRA. 

Recovery Window goal (which drives the space utilization)

The recovery window goal is set at the policy level, and this value (in days) is the number of days that you want to keep as a recovery window for all databases that are a member of this policy.  This will drive the space utilization.

Total space

The ZDLRA comes with all the space pre-allocated.  When you are looking at OEM, or in the SAR report you will see the total space listed. You want to make sure that you have enough space for your database backups and any incoming new backups.

Used Space

When the ZDLRA purges backups beyond the the Recovery Window Goal that you set, if does a bulk purge of backups.  This can be controlled by setting the maximum disk backup retention in days (which defaults to 1.5 times the recovery window goal).  Because of the bulk purge, more space is shown as used than is needed to support your recovery window goal.

Recovery Window Space

This is the amount space that is needed to support the recovery window goal.  Because, of the bulk purge, the recovery window space is less than the used space.

Reserved space

In order to control what happens with space, the concept of reserved space is used.  When a database is added to the ZLDRA, the reserved space value is set for this database.  This value should be updated regularly to ensure that there is enough space for the database backups to be stored.

The important things to know about reserved space are:

• The sum of all the reserved space cannot be greater than the total space available on the ZDLRA.
• When adding a new database, it's reserved space must fit within the unreserved space.
• When a new database is added, the reserved space must be set to least the size of the database, and defaults to 2.5 times the size of the database.
• The reserved space for a database needs to be at least the size of the largest datafile.
• The reserved space should be larger than the amount of space needed to support the recovery window goal space for the database.  For databases with fluctuation, you need to reserve space for the peak usage. 

The reserved space serves two purposes when properly set

1. It can be used to determine how much space is available for new database backups.
2. If the ZDLRA determines that it does not have enough space to support the recovery window goal of the supported databases, space is reclaimed from databases whose reserved space is too small.

It is critical to keep the reserved space updated, and many customers have used an automated process to set the reserved space to "recovery window space needed" + 10%

Unfortunately configuring an automated process for all databases does not take into account any fluctuations in usage.  Let's say I have a database which is much busier at months end, I want to make that sure my reserved space is not adjusted down to the low value, I want it to stay adjusted based on the highest space usage value.

Autotuned_reserved_space 

This where autotuned reserved space can help you manage the reserved space.  This setting is controlled at the policy level.  

AUTOTUNED_RESERVED_SPACE

This value is set at the protection policy level and contains either "YES" or "NO", and defaults to "NO". "YES" will allow the ZDLRA to manage reserved space automatically for all databases (whose disk_reserved_space is not set) and are a member of this policy.

MAX_RESERVED_SPACE

This value is also set at the protection policy level.  This value is optional for autotuned_reserved_space, but if set, it will control the maximum amount of reserved space that can be set for an individual database in the protection policy. 

AUTOTUNE_SPACE_LIMIT

This value is set at the storage level for ALL databases. This sets a reserved space usage limit, where autotuning can slow down large reserved space increases. When reached, autotune will limit databases from increasing their reserved space growth to 10% per week.  This value is optional and will default to the total space if not set.  

SUMMARY:

• autotuned_reserved_space - Enables autotuning of space within a protection policy
• max_reserved_space - Controls the maximum reserved space of databases in a protection policy
• autotune_space_limit - Slows the reserved space growth when a specified space limit is reached.

What does autotune reserved space do ?

• On a regular basis, if needed, the reserved space for each autotune controlled database is adjusted to reserve space for the recovery window goal, and incoming backups.

• If the database has a disk_reserved_space set, autotuning will not be used for this database.  It is assumed that the disk_reserved_space will be set manually for this database

Autotune  will replace the need for the ZDLRA admin to constantly update the reserved space for each database, as it's space needs change over time. It will also allow them to configure a constant reserved space for databases with fluctuating storage usage.