Quantum 3.1.4.1 manual RAID Cache Configuration, RAID Write-Back, Caching

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StorNext File System Tuning The Underlying Storage System

RAID Cache

Configuration

The single most important RAID tuning component is the cache configuration. This is particularly true for small I/O operations. Contemporary RAID systems such as the EMC CX series and the various Engenio systems provide excellent small I/O performance with properly tuned caching. So, for the best general purpose performance characteristics, it is crucial to utilize the RAID system caching as fully as possible.

For example, write-back caching is absolutely essential for metadata stripe groups to achieve high metadata operations throughput.

However, there are a few drawbacks to consider as well. For example, read-ahead caching improves sequential read performance but might reduce random performance. Write-back caching is critical for small write performance but may limit peak large I/O throughput.

Caution: Some RAID systems cannot safely support write-back caching without risk of data loss, which is not suitable for critical data such as file system metadata.

 

Consequently, this is an area that requires an understanding of

 

application I/O requirements. As a general rule, RAID system caching is

 

critically important for most applications, so it is the first place to focus

 

tuning attention.

 

 

RAID Write-Back

Write-back caching dramatically reduces latency in small write

Caching

operations. This is accomplished by returning a successful reply as soon

 

as data is written into cache, and then deferring the operation of

 

 

actually writing the data to the physical disks. This results in a great

 

performance improvement for small I/O operations.

 

Many contemporary RAID systems protect against write-back cache data

 

loss due to power or component failure. This is accomplished through

 

various techniques including redundancy, battery backup, battery-

 

backed memory, and controller mirroring. To prevent data corruption, it

 

is important to ensure that these systems are working properly. It is

 

particularly catastrophic if file system metadata is corrupted, because

 

complete file system loss could result. Check with your RAID vendor to

 

make sure that write-back caching is safe to use.

 

Minimal I/O latency is critically important for metadata stripe groups to

 

achieve high metadata operations throughput. This is because metadata

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StorNext File System Tuning Guide

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Contents StorNext Copyright Statement Contents Contents StorNext File System Tuning Underlying Storage SystemRAID Cache Configuration RAID Write-BackCaching RAID Read-Ahead RAID Level, Segment Size, and Stripe Size File Size Mix and Application I/O Characteristics Buffer Cache NFS / CifsSnfs and Virus Checking Metadata NetworkMetadata Controller System FSM Configuration File Settings Stripe GroupsAffinities StripeBreadth BufferCacheSize InodeCacheSizeThreadPoolSize ForcestripeAlignment FsBlockSizeJournalSize FsBlockSize JournalSizeSnfs Tools StorNext File System Tuning Metadata Controller System StorNext File System Tuning Metadata Controller System Latency-testindex-number seconds Mount Command Options Distributed LAN Disk Proxy Networks Snfs External APIHardware StorNext File System Tuning Guide Network Configuration and Topology SwitchDistributed LAN Servers Distributed LAN Client Vs. Legacy Network Attached StorageFault tolerance PerformanceLoad Balancing Client Scalability Windows Memory Requirements Robustness and Stability Consistent Security ModelStorNext File System Tuning Windows Memory Requirements Sample FSM Configuration File StorNext File System Tuning Sample FSM Configuration File StorNext File System Tuning Sample FSM Configuration File StorNext File System Tuning Sample FSM Configuration File StorNext File System Tuning Sample FSM Configuration File StorNext File System Tuning Sample FSM Configuration File