Caching & Tiering BPG

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1 Intro: SSD Caching and SSD Tiering functionality in the StorTrends 3500i offers the most intelligent performance possible from a hybrid storage array at the most cost-effective prices in the industry. StorTrends leverages SSD caching and tiering technologies together to ensure flash-level performance throughout the life of the array while increasing the lifespan of drives throughout the system. While the SSD Cache quickly promotes data, the SSD Tier promotes data using auto-tiering capability - delivering instantaneous and sustained performance for the most critical blocks within the IT environment. Additionally, hard drives within hybrid configurations are optimized to migrate the most frequently accessed blocks within each disk platter to the outer tracks to ensure that the performance is maximized, even at the lowest levels of the array. This document is designed to inform users of the 3500i capabilities while assisting users in tuning their array to realize the highest performance possible.. Volume Profile: StorTrends offers many options within volume creation to give users the capability to adjust their system based on their unique requirements. These options and descriptions of each can be found within the ManageTrends GUI. Databases, linked clones and any other high performance volumes typically reside within the SSD tier to achieve the highest performance, so a High profile would be the optimal setting. In hybrid configurations, SSD capacity can be a limitation. For example, if there is 20TB of data and the vast majority of this data requires solid-state performance, this will not be possible. If the differentiation between volumes is nominal IO-wise, then focus on placing volumes with heavier write loads within the SSD tier to minimize writes to spinning disk. A minimal heavier write load would be a 50% read and 50% write. Higher write percentages should yield a higher SSD priority. This is the reason for additional options.

2 The next level is a Medium profile. The only instance that a Medium profile comes into play is when there are more than 2 levels. Normally, this fits as a 15k SAS tier between the performance of SSD and 7.2k spinning disks. If you purchase an expansion shelf of 15k SAS drives and add it into a standard SSD/NL-SAS (7.2k) hybrid array, these volumes would promote up from the NL-SAS tier to the new shelf. The volumes that would get selected for this are volumes for applications with larger block sizes such as Exchange or SharePoint. This is also a great choice for critical (not high performance, but not low performance) VMs. Of course, we do have alternatives in later sections to handle the not high / low performance situations in a standard hybrid configuration. The last option is to just give capacity to applications that don t have any special requirements other than to be available or are known to be highly sequential in nature. This ensures that you are not wasting any space in your SSDs. Examples of this are infrastructure VMs like DHCP, DNS or AD servers and also any VTL, DR snapshots or direct backups that need to be stored. To pin a similar type volume to this you would select the last, but not least, important Low profile. Cache: Since not all I/O is rarely only read or written, the SSD cache space within the StorTrends 3500i is split into a RAID 0 read cache and a RAID 1 write cache to catch all I/O that would direct to the slower spinning disk tiers. One of the StorTrends advantages with SSD caching is that none of the blocks located in the SSD tier are duplicated in the SSD cache and vice versa maximizing the amount of unique data among the SSD drives. Another major advantage is the ability to monitor block access within the SSD cache to ensure that the least-accessed blocks are first cleared from the cache before adding newer (higher priority) data.

3 If a user requires all or almost all of a volume to reside within the SSD tier for optimal performance of all data within the volume, they can set the volume to have a High profile and can also select the option to Cache All IO. StorTrends will recognize this as a high priority volume within the tier, so if some blocks are demoted to a lower tier due to no access, the cache will be used to immediately give SSD performance to demoted data once accessed. This also will cover the case of the SSD tier being completely full, forcing any new IO to go to lower tiers and slow down the volume s effective response time. Another option for caching is to give medium performance volumes (medium or low tier) the availability to speed up when accessed, but not guarantee the high SSD tier performance. In this case, the IO for this volume should not be higher writes. This is because the data must be written to the cache (immediate high performance) and then unavoidably rewritten a second time to disk, creating overall disk inefficiency if consistently occurring. StorTrends does write this dirty cache data sequentially to ensure that performance is hindered minimally. StorTrends also offers options to easily expand or decrease cache capacity depending on users performance demands. If the SSD write cache becomes completely full, the write cache can simply be expanded to allocate more RAID 1 space. If the SSD write cache is completely empty or not fully utilized with the read cache full, then the amount of write cache can be reduced to conversely increase the RAID 0 space for further read cache capacity. Another option in this case would be to only Accelerate Random I/Os on the volume page shown below. Additionally, if both the read and write cache are constantly full, StorTrends offers the option to upgrade SSD drives to higher capacities with zero downtime. Not only is StorTrends performance- focused, but it is highly versatile to ensure that the array can mold to an everchanging environment. NOTE: As a best practice, any volumes configured to allow access into the SSD cache should be configured to Accelerate Random I/Os. This will ensure optimal use of the SSD cache by avoiding sequential I/Os to be cached, which are bandwidth dependent, not I/O dependent.

4 Initial Deployment Alternative: Often times, the projected workloads of the volumes that will reside on the array are uncertain during initial setup and deployment. StorTrends offers a few options to avoid workload uncertainty and provide flash performance even when volume profiles have not been set. The first option is the StorTrends idata tool that can be downloaded free of charge from and will give the performance for all server aspects such as CPU, memory, throughput, block size, disk IO, and much more. This information can then be utilized to gauge performance requirements for volumes to be placed on the SAN. The next option is to manage the volume profiles during implementation to ensure that the heaviest and most accessed blocks promote up to the SSD tier. This will also work for optimizing the SSD tier space as the only blocks

5 that will enter will be recently accessed data. Of the recently accessed, StorTrends Tiering algorithms first promote the highest accessed blocks to ensure that the most critical blocks are within the SSD Tier first and foremost. While waiting on the tiering to promote blocks, the SSD caching can cover the accesses in the interim. This is easily completed by following the steps below: Promote volumes to tier: 1. Volume Wizard: Create volumes No Accelleration and a Low or Medium tier profile. 2. Migrate Data: Connect, format and migrate data to the new volume. 3. Configure Performance: From the volume page, set Accelerate Only Random IOs and a High profile. By following these steps, the performance will be slightly limited for re-accessed blocks, but once in the cache the performance will increase exponentially from the spinning disk tiers and also all new data will go directly into the SSD tier. That being said, only the most critical blocks enter into the SSD tier and the space is completely maximized. An additional setting that can be configured to optimize the space is the tier policy settings. You can get to these by selecting the storage pool on the left-hand pane and then scrolling down to the bottom of the main pane. The demotion policy is set for 1 week by default and basically forms a retention in the SSD tier. The lowest optimal setting (especially for VDI) is 4 days to encompass long weekend situations. Make sure that you click the checkmark on the right after changing the setting. The other policy is the promotion policy that can be seen by selecting the up arrows to the right of where it says Demotion. What we expect to see in the ILM chart on the next page, is the Class 3 (over a day) data in Tier 1 reduce by half. The promotion policy defaults at 32 and usually can be increased to reduce what gets promoted to the SSD tier. After a few days of running on the StorTrends unit, you can see how many times your blocks are accessed. From the Information Lifecycle Management SRM chart (left-hand pane; bottom of the Storage Pool options), there will be class 6 or higher blocks. The general mark is 1K, so anything over that exceeds the amount of movement to expect StorTrends to promote. The lower mark is 125, so lower than this will be minimally affective, but this is potentially better than looking at the high mark of 1k. Looking at the ILM chart on the next page and looking at Tier 2 [Hot Medium], we see class 5 (Accessed 1-99 times within the last hour 32+ accesses by default are up for promotion) with accesses over 1k. Since this is less feasible to promote, we look at the class 6 territories of Tier 2 and there is a total of 844 (including the class 7: 10). That being under / near the 1k mark, we will only promote the class 6 and higher accesses by setting the Promotion from 32 to 100. The 100 comes from the class 6 value within the legend on the right of the ILM chart on the next page.

6 Full SSD Capacities: The process before can also be used in the event that the SSD tier becomes full and new volumes are created requiring SSD space. The SSD tier can easily become full considering the limited capacities of SSDs today. There are a few options to relieve the SSD tier of space, including setting lesser important volumes to the Low tier profile and reducing the snapshot frequencies. Please note that once a volume s block is in the SSD tier and being accessed at least once an hour, it will not demote even though the volume is changed to be a Low profile. This is important since the tier is full and blocks have to demote to make space for others to promote. As stated before the caching settings can be changed to increase either your read or write cache in the event that one or the other is always seemingly full. In case the SSD tier is full then an expansion shelf can be added to the unit to give you the additional SSD capacity that your environment has grown into. Performance Storage. Proven Value. American Megatrends Inc. ami.com 5555 Oakbrook Parkway, Bldg. 200 Norcross GA Sales & Product Information StorTrendsSales@ami.com Technical Support stortrends-support@ami.com stortrends.com CERTIFIED Performance Storage. Proven Value American Megatrends Inc. - Specifications subject to change without notice