Whitepaper: ReadyNAS FlexRAID Volume Optimization Guide

Whitepaper:
Optimizing Your ReadyNAS® OS Flex-RAID Volumes
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5.3. Sequential Read and Write Performance on SMB Volumes
In the sequential read and write test, RAID 6 performs best for sequential reads, while RAID 60 has the best balance of read
and write performance.
Figure 5.3: Volume Performance and Configuration on ReadyNAS Platform
6. Overview of ReadyTIER
Using ReadyTIER, you can create a higher performing RAID
group consisting of SSD drives in collaboration with spindle
hard drives. When you create a tier, you tell ReadyNAS OS to
utilize the tier for storing either data or metadata.
When deciding to create a data tier or a metadata tier, you
need to take into consideration how data will be read and
written, how often, and decide where you want to see a
performance increase.
Metadata tiering is beneficial for use cases were data is
added onto files in small increments, like databasing, and
does not migrate from the SSD tier (aka, the highest tier) to
the spindle tier (lowest tier) when reaching capacity. Data
tiering provides the same benefits as metadata tiering, but
all new data is written to the SSD tier first allowing for an
accumulated amount of recent data to reside on the SSD tier.
Recently written data will come from the SSD tier rather than
the spindle tier. While metadata will continue to accumulate
on the SSD tier, data will migrate to spindle when either the
volume reaches a customizable capacity (default at 90% of
the SSD tier limits), or when triggered via a scheduled task,
or when migrated manually.
Metadata Tiering: Stores directory information, file names,
file permissions, file updates under 8Kb of data, and data
checksums to SSDs to make metadata lookup faster. Persists
on the SSD tier.
Data Tiering: Metadata tiering and all new data is written to
the SSD tier and migrated to the spindle RAID tiers later.
For ReadyTIER, what is meant by data versus metadata?
The Btrfs file system, the basis of the ReadyNAS OS file
system, organizes information stored in the file system as
data and metadata (and system data, but that isn't relevant
here). Volume metadata includes such things as directory
information, file names, file permissions, stores under 8Kb of
data, and checksums. Volume metadata is read and written
more frequently than specific blocks of data and there is
typically much less metadata than data.