D-Link DSN-626 User Manual - Page 135

I/O Type, Block Size, Sectors, Populate-on, Read Threshold, Database, 1MB 2

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D-Link Document - User Manual the application to get the best performance. If the above three applications are not suitable, the last item is customization which you may set the configurations by yourself. I/O Type Database File System Web Service Customization Block Size (Sectors) 1MB (2,048) 2MB (4,096) 4MB (8,192) 1MB/2MB/4MB Sub-block Size (Sectors) 8KB (16) 16KB (32) 64KB (128) 8KB/16KB/64KB Populate-onRead Threshold 2 2 2 ≥ 0 Populate-onWrote Threshold 0 2 0 ≥ 0 The block size affects the cache use and the warm up time. The cache use shows how much of the allocated cache actually holds the user data. And the warm up time is the process of how long to fill the cache. You can image that the highest cache use is obtained when all of the frequently reread data is located very close to other data that is frequently re-read. Using a larger cache block size of I/O type is more useful to performance than a smaller one. Conversely, when frequently reread data is located far from other data that is frequently reread, the lowest cache use is obtained. In this case, the lowest cache block size of I/O type allows the most user data to be cached. The sub-block size affects the cache warm up time, too. A larger sub-block size causes a cache to fill more quickly than a smaller one, but it can also affect the response time of host I/O. Also resources occupying the system, such as CPU utilization, memory bandwidth, or channel utilization. A very high locality of reference can be more useful from a larger sub-block size than from a smaller one, especially if those blocks that are reread frequently reside in the same subblock. This occurs when one I/O causes the sub-block to be populated and another I/O in the same sub-block gets a cache hit. These are tradeoffs depending on the applications. Users may set them by experience to get the best performance. Here we provide a formula which can calculate the estimated warm up time. We define that  T: Warm up time; seconds required.  I: Best random IOPS of HDD.  S: I/O Size.  D: Number of HDDs.  C: Total SSD caching capacity.  P: Populate-on-read or Populate-on-write threshold We assume that random read/write from HDD to achieve the capacity of SSD should be Copyright@2014 D-Link System, Inc. All Rights Reserved. 135

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D-Link Document – User Manual
the application to get the best performance. If the above three applications are not suitable, the
last item is customization which you may set the configurations by yourself.
I/O Type
Block Size
(Sectors)
Sub-block Size
(Sectors)
Populate-on-
Read Threshold
Populate-on-
Wrote Threshold
Database
1MB (2,048)
8KB (16)
2
0
File System
2MB (4,096)
16KB (32)
2
2
Web Service
4MB (8,192)
64KB (128)
2
0
Customization
1MB/2MB/4MB
8KB/16KB/64KB
≥ 0
≥ 0
The block size affects the cache use and the warm up time. The cache use shows how much of the
allocated cache actually holds the user data. And the warm up time is the process of how long to
fill the cache. You can image that the highest cache use is obtained when all of the frequently
reread data is located very close to other data that is frequently re-read. Using a larger cache block
size of I/O type is more useful to performance than a smaller one. Conversely, when frequently
reread data is located far from other data that is frequently reread, the lowest cache use is
obtained. In this case, the lowest cache block size of I/O type allows the most user data to be
cached.
The sub-block size affects the cache warm up time, too. A larger sub-block size causes a cache to
fill more quickly than a smaller one, but it can also affect the response time of host I/O. Also
resources occupying the system, such as CPU utilization, memory bandwidth, or channel
utilization. A very high locality of reference can be more useful from a larger sub-block size than
from a smaller one, especially if those blocks that are reread frequently reside in the same sub-
block. This occurs when one I/O causes the sub-block to be populated and another I/O in the same
sub-block gets a cache hit.
These are tradeoffs depending on the applications. Users may set them by experience to get the
best performance. Here we provide a formula which can calculate the estimated warm up time.
We define that
T: Warm up time; seconds required.
I: Best random IOPS of HDD.
S: I/O Size.
D: Number of HDDs.
C: Total SSD caching capacity.
P: Populate-on-read or Populate-on-write threshold
We assume that random read/write from HDD to achieve the capacity of SSD should be
135
Copyright@2014 D-Link System, Inc. All Rights Reserved.