8. SSD Profiling Tool
SSD Profiling Tool controls the creation and execution of SSD over-provisioning tests. These tests help
determine the optimum amount of SSD over-provisioning to set when creating an SSD RAID group.
SSD Over-Provisioning
When an SSD is full, the disk's firmware frees up space in a process called garbage collection. Garbage
collection results in an effect called write amplification, which reduces the lifespan and random write
performance of the SSD. Write amplification can be reduced by over-provisioning, which means reserving
space on the disk for garbage collection. Most SSDs are manufactured with 7% or more of their capacity
reserved for over-provisioning.
SSD Extra Over-Provisioning
SSD Extra Over-Provisioning enables to you reserve additional space for over-provisioning at the RAID level
when creating an SSD RAID group in QTS. Reserving extra space can increase the consistent random write
performance and lifespan of the SSD group.
Important
• Space reserved for SSD Extra Over-Provisioning cannot be used for data storage. The
total storage capacity of the SSD RAID group will be reduced by the specified amount.
• SSD Extra Over-Provisioning can only be enabled during RAID group creation.
• After creating a RAID group with SSD Extra Over-Provisioning enabled, you can
disable the feature or decrease the amount of reserved space. It is not possible to
increase reserved space.
• Results will vary depending on the SSD model. Enabling SSD Extra Over-Provisioning
may have no effect on some SSDs.
SSD Over-Provisioning Tests
During an SSD over-provisioning test, SSD Profiling Tool first fills the SSDs with random data. It then tests
the random write performance of the SSDs over several test phases, each using a different amount of over-
provisioning. For example, if a test is created with a test range of 0-20% and a test interval of 5%, SSD
Profiling Tool will test SSD write performance in 5 phases, with over-provisioning set to 0%, 5%, 10%, 15%,
and 20%. If the random write performance of the disk is very low during any phase, SSD Profiling Tool will
end the phase early and move to the next one.
Creating an SSD Over-Provisioning Test
1. Go to SSD Profiling Tool > Review .
2. Click + Create Test.
The Create SSD Test wizard opens.
3. Click Next.
4. Optional: Select an expansion unit from the Enclosure Unit list.
Important
• You cannot select disks from multiple expansion units.
QTS 4.5.x User Guide
SSD Profiling Tool 331
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