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Data access settings can be configured at the pool (or even the single file) level to optimize data access for the type of application accessing it. Data can be optimized for concurrent, streaming, or random access. Each of these settings changes how data is laid out on disk and how it is cached.
Data access setting | Description | On-disk layout | Caching |
Concurrency | Optimizes for current load on the cluster, featuring many simultaneous clients; this setting provides the best behavior for mixed workloads | Stripes data across the minimum number of drives required to achieve the data protection setting configured for the file. | Moderate prefetching |
Streaming | Optimizes for high-speed streaming of a single file, for example to enable very fast reading with a single client | Stripes data across a larger number of devices. | Aggressive prefetching |
Random | Optimizes for unpredictable access to the file by performing almost no cache prefetching | Stripes data across the minimum number of drives required to achieve the data protection setting configured for the file | Little to no prefetching |
As the settings indicate, the ‘Random’ access setting performs little to no read-cache prefetching to avoid wasted disk access. This works best for workload with only small files (< 128 KB) and large files with random small block accesses.
Streaming access works best for sequentially read medium to large files. This access pattern uses aggressive prefetching to improve overall read throughput, and on disk layout spreads the file across many disks to optimize access.
Concurrency (the default setting for all file data) access is the middle ground with moderate prefetching.
Concurrency is the preferred access setting for mixed workloads.
The attributes of a particular directory or file can be viewed by running the following command and replacing data in the example with the name of a directory or file. The command’s output below, which shows the properties of a directory named ‘data’, has been truncated to aid readability:
# isi get -D data
POLICY W LEVEL PERFORMANCE COAL ENCODING FILE IADDRS
default 4x/2 concurrency on N/A ./ <1,36,268734976:512>, <1,37,67406848:512>, <2,37,269256704:512>, <3,37,336369152:512> ct: 1459203780 rt: 0
*************************************************
* IFS inode: [ 1,36,268734976:512, 1,37,67406848:512, 2,37,269256704:512, 3,37,336369152:512 ]
*************************************************
* Inode Version: 6
* Dir Version: 2
* Inode Revision: 6
* Inode Mirror Count: 4
* Recovered Flag: 0
* Restripe State: 0
* Link Count: 3
* Size: 54
* Mode: 040777
* Flags: 0xe0
* Stubbed: False
* Physical Blocks: 0
* LIN: 1:0000:0004
* Logical Size: None
* Shadow refs: 0
* Do not dedupe: 0
* Last Modified: 1461091982.785802190
* Last Inode Change: 1461091982.785802190
* Create Time: 1459203780.720209076
* Rename Time: 0
* Write Caching: Enabled
* Parent Lin 2
* Parent Hash: 763857
* Snapshot IDs: None
* Last Paint ID: 47
* Domain IDs: None
* LIN needs repair: False
* Manually Manage:
* Access False
* Protection True
* Protection Policy: default
* Target Protection: 4x
* Disk pools: policy any pool group ID -> data target x410_136tb_1.6tb-ssd_256gb:32(32), metadata target x410_136tb_1.6tb-ssd_256gb:32(32)
* SSD Strategy: metadata
* SSD Status: complete
* Layout drive count: 0
* Access pattern: 0
* Data Width Device List:
* Meta Width Device List:
*
* File Data (78 bytes):
* Metatree Depth: 1
* Dynamic Attributes (40 bytes):
ATTRIBUTE OFFSET SIZE
New file attribute 0 23
Isilon flags v2 23 3
Disk pool policy ID 26 5
Last snapshot paint time 31 9
*************************************************
* NEW FILE ATTRIBUTES
* Access attributes: active
* Write Cache: on
* Access Pattern: concurrency
* At_r: 0
* Protection attributes: active
* Protection Policy: default
* Disk pools: policy any pool group ID
* SSD Strategy: metadata-write
*
*************************************************
Here is what some of these lines mean:
OneFS command to display the file system properties of a directory or file.
Write caching (SmartCache) is turned on.
The SSD strategy is set to metadata-read.