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Analyst Perspective: SSD Caching or SSD Tiering - Which is Better?
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Analyst Perspective: SSD Caching vs. SSD Tiering – Which Is Better? Dennis Martin President, Demartek Santa Clara, CA August 2012 1
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First there was HSM, and then came ILM. But, now that SSDs are gaining in acceptance, automated tiering for SSDs and SSD caching are getting much more serious consideration. Shrinking storage budgets and escalating capacity requirements have made it clear that storage must be managed better. One of the basics of good management is ensuring that data is kept on the most appropriate storage according to its usefulness and importance to the organization. In this session we will compare SSD automated storage tiering and SSD caching, showing commonalities and the differences as well as the advantages and disadvantages of each type of technology. Included will be discussions of hardware and software solutions.
Transcript of Analyst Perspective: SSD Caching or SSD Tiering - Which is Better?
Analyst Perspective: SSD Caching vs.
SSD Tiering – Which Is Better?
Dennis Martin
President, Demartek
Santa Clara, CA
August 2012
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About Demartek
Santa Clara, CA
August 2012
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Industry analysis with on-site test lab
Lab includes servers, networking and storage • Fibre Channel – 4, 8, & 16 Gbps
• Ethernet – 1 & 10 Gbps – NFS, CIFS, iSCSI & FCoE
• Servers – 8+ cores, large RAM
• Virtualization – ESX, Hyper-V, Xen
We prefer to run real-world applications to test servers and storage solutions • Currently testing various SSD and other technologies
Website: www.demartek.com
Background and Assumptions
Santa Clara, CA
August 2012
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The concepts described in this presentation apply to NAND flash and apply to future “storage class memory” technologies
Because this presentation focuses on enterprise solutions, and is not limited to NAND flash, I refer to SSD technology
Many enterprise solutions require: • High-endurance – many writes
• High-performance – fast
• Ideally both high-endurance and high-performance
Data Placement in the Enterprise
Santa Clara, CA
August 2012
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Two basic choices • Use the SSD as primary or direct storage
• Use the SSD as a cache in front of HDDs
• Some solutions do both
Data placement choice is independent of: • SSD location – server, network, or storage array
• SSD form factor – PCIe card, drive form-factor, DIMM form-factor, BGA, etc.
SSD as Primary Storage
Santa Clara, CA
August 2012
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User decides what data to place on the SSD
User decides when to place data on the SSD
User moves the data to the SSD and updates applications to point to the new location
SSD benefits only those applications that use data placed on the SSD
Performance improves instantly
Problems with SSD as Primary Storage
Santa Clara, CA
August 2012
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Consider a system with two applications • Application one is highest priority 75% of the time
• Application two is highest priority 25% of the time
• Not enough SSD to handle both
• User manually places the data for application one on the SSD, then later has to remove that data to put data for application two onto the SSD.
Now imagine dozens, hundreds or more applications • This requires automation or “auto-tiering” software
Auto-Tiering Solution
Santa Clara, CA
August 2012
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Observes I/O patterns over a period of time • Can ignore certain times of day, certain types of I/O
Based on policies set by the administrator, moves data to appropriate tier • Data movement occurs at time specified by
administrator
A volume can be composed of multiple tiers of storage • Tiers are often: SSD, 15K/10K, 7200 RPM
Different solutions use different “chunk” sizes
SSD as a Cache
Santa Clara, CA
August 2012
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Caching solution identifies frequently accessed (“hot”) data
Caching solution automatically moves a copy of the hot data to the SSD cache
Multiple applications can benefit from the SSD cache simultaneously
Performance improves over time, as cache is populated with data (“warm-up”)
Some caching solutions only cache reads, others cache both reads and writes
SSD Caching Implementations
Santa Clara, CA
August 2012
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Multiple implementations • Host-based software, stand-alone or in an application
• Packaged with RAID controllers
• External caching appliances
• Inside storage arrays
Host-based RAID controller Caching appliance
Storage system
SSD Caching Solutions
Santa Clara, CA
August 2012
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SSD form factors • Host-based often can use any SSD, some can use
RAM together with the SSD as a cache
• Hardware-based may have more limited choices
• Some solutions can use multiple SSDs
Generally no application changes are required
SSD Caching Workloads
Santa Clara, CA
August 2012
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Cache Friendly workloads • Hot spots with repeated access
• OLTP databases
• Database indexes
• File system table of contents (MFT, inodes, etc.)
Cache Un-friendly workloads • Data is accessed approximately evenly and is larger
than the cache
SSD Cache Read/Write “Flip”
Santa Clara, CA
August 2012
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We see this frequently with read-only caches • The cache warms with read data
• The back-end storage sees fewer reads
• The back-end storage processes more writes
I/O
pe
r S
ec
on
d (
IOP
S)
Time
Read/Write "Flip" with SSD Caching
Total Writes Reads
Conclusion
Santa Clara, CA
August 2012
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Both caching and tiering are effective at improving enterprise workload performance
Some vendors who started with one are offering the other
Caching is easier to manage
Caching reacts immediately to accelerate performance and does not need to wait for scheduled data movement
Tiering solutions consume back-end storage IOPS during data movement but caching solutions do not
References
Santa Clara, CA
August 2012
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Demartek SSD Zone www.demartek.com/SSD
Demartek SSD Deployment Guide • Search for “SSD Deployment Guide”
• www.demartek.com/Demartek_SSD_Deployment_Guide.html
