Auto Tiering (QTiering 2.0)
QSAN Auto Tiering (QTiering) is an automated storage tiering solution that automatically places hot data on SSD or faster hard drives (performance tier) and cold data on lower cost high-capacity drives (capacity tier), allowing you to optimize application performance without straining your budget or sacrificing capacity. Auto tiering is a licensed feature available on the XCubeSAN series.
Storage Efficiency on Demand
From the perspective of storage features, the performance of SSD is high, but the cost is also high per GB. Relatively speaking, the cost of traditional hard drive is low, so as performance is relatively poor. If we follow the 80/20 rule to configure storage systems, all-SSD configuration is unreasonable for all but the most intensive applications. On the other hand, the data itself has a lifecycle. As the age of the data increases, it is accessed less often.

Therefore, to balance performance and cost factors, adapting a hybrid storage architecture with a mixture of SSD and traditional HDD seems to be the most reasonable approach for modern IT environments. An automated tiering pool is a simple and elegant solution for dynamically matching storage requirements with changes in the frequency of data access.
3 Levels of Tiered Storage
QTiering supports 3 tiers of different drive types.
  • Tier 1: SAS/SATA* 2.5” SSD drive
  • Tier 2: 15K/10K 3.5”/2.5” SAS drive
  • Tier 3: 7.2K near-line 3.5”/2.5” SAS drive
Auto Tiering Architecture
A newly created auto tiering pool is based on thin provisioning technology. Each tier works based on one or more disk groups. To increase the capacity of an auto tiering pool, any tier (disk group) which contains either one tier of SSDs, SAS HDDs, or NL-SAS HDDs can be added to the pool any time. The following is the storage architecture of an auto tiering pool.
Flexible RAID & Disk Configurations
Auto Tiering 2.0 supports flexible RAID and disk configurations. You can create each tier (disk group) with different RAID level and different quantity of disk. For example, SSD tier uses 4 disks with RAID 10 for extreme performance, SAS tier uses 6 disks with RAID 6, and NL-SAS tier uses 8 disks with RAID 5 for capacity. This feature is very important for IT administrator to arrange storage plan flexibly.
Intelligent QTiering Mechanism
QTiering, an auto tiering storage management system, manages the data relocation and monitors the data hotness ratio using half-life coefficient and advanced ranking algorithm. QTiering operates on three major functions.
  • Sub-LUN Statistics
    The volume is divided into 1GB units, which is called a sub-LUN. This is the basic unit of data movement among tiers. Whenever there are I/O requests, the activity level of a sub LUN is determined by counting the read and write frequency to the sub-LUN.

  • Ranking Algorithm
    Access records of each sub-LUN are collected and analyzed every hour. LVM maintains a cumulative I/O count and weighs each I/O by how recently it arrived, using a half-life coefficient. The ranking algorithm then uses these statistics to calculate the percentage of hot data.

  • Data Movement
    The data relocation engine then uses these percentages as guidance to move sub-LUNs between storage tiers automatically. The data relocation process will not stop I/O services. When data relocation begins to move sub-LUNs from slower tier to the faster tier, you will notice the I/O performance increases over time.
Well Defined Tiering Policies
For a best performance in various environments, auto tiering has a completely automated feature that implements a set of tiering polices. Tiering policies determine how new allocations and ongoing relocations should apply within a volume for those requirements.
  • Auto Tiering (Default)
    Sets the initial data placement to the optimized tier (disk group) and then relocates the data based on the statistics such that data is relocated among tiers according to the I/O activity.

  • Start Highest then Auto Tiering
    First sets the preferred tier for the initial data placement to the highest tiers with available space, then relocates the data based on the statistics and the auto tiering algorithm.

  • Highest Available Tier
    Sets the preferred tier for the initial data placement to the highest tiers with available space, and so as the succeeding data relocation.

  • Lowest Tier
    Sets the preferred tier for the initial data placement to the lowest tiers with available space, and so as the succeeding data relocation.

  • No Data Movement
    Sets the preferred tier for the initial data to the optimized tier, and retain the data without movement.
Benefits of Using QTiering Technology
  • Flexible Configurations
    IT administrator can arrange the storage plan flexibly by QTiering flexible architecture. And also easy to setup by the intuitive SANOS 4.0 web UI.

  • Optimal Storage Efficiency
    According to the data access frequency, continue optimizing the data across extreme performance SSD (SSD tier), performance SAS HDDs (SAS tier), and high-capacity NL-SAS HDDs (NL-SAS tier).

  • Cost Saving
    Purchasing only the required SSDs can lower the TCO (Total Cost of Ownership).

  • High performance
    Intelligently managing data placement can increase performance by moving the hot data to the performance tier.

  • Schedule Relocation
    The relocation of auto tiering can be scheduled during off-peak hours to avoid affecting the system performance in office hours.

  • Tiering Analysis
    By monitoring the tiering status on each pool, you can dynamically adjust to more accurate policy.
Ideal for Data Center Environments
SANOS with QTiering technology provides a solution to achieve optimal storage efficiency and improved performance, making it the most cost effective storage solution for data center environments with dynamic workload changes.
SSD Cache vs. Auto Tiering
A key difference between tiering and cache is that tiering moves data to SSD instead of simply caching it. Tiering can also move data both from slower storage to faster storage and vice versa. But SSD cache is essentially a one-way transaction. The important difference between moves and copies is that a cache does not need to have the redundancy that tiering does.
Total storage capacity in auto tiering is a sum of all individual tier capacities whereas in cache, the cache capacity does not add to the overall slower storage capacity. This is one of the key differences. In addition, SSD cache affects more rapidly than auto tiering because auto tiering will take effect after data relocation. So SSD cache warm-up timeframe is usually minutes/hours whereas tiering warm-up is usually in days.
SSD cache is used for highly frequent data access environment and is effective in a short term such as virtualization or video editing applications. However, auto tiering is used for predictable I/O workloads and is effective in a long term. It's suitable for web, file, or email server applications.
 SSD CacheAuto Tiering
Total CapacityHDDHDD + SSD
When SSD is DamagedPool Works FinePool Fails
PerformanceEffective in Short TermEffective in Long Term
Best Practice
Here is a suggestion of best practice. First of all, you may know the total capacity, and better to know how much hot data your application uses.
  • SSD Tier ($$$)
    Suggest SSD tier using at least 4 disks with RAID 10 for extreme performance. Prepare SSD storage capacity in 10% to 15% of the total pool capacity to fulfill the requirements of critical high I/O applications.

  • SAS Tier ($$)
    Suggest SAS HDD tier configuring with RAID 6. And preparing around 30% of the total storage capacity.

  • NL-SAS Tier ($)
    For capacity tier, suggest NL-SAS HDD using RAID 5 level to store cold data. This tier occupies the rest of the storage capacity.
Suggest using "Auto Tiering" policy when creating a volume, and the relocation schedule remains in daily. These configurations show the best performance for auto tiering.