Intel Computer Hardware SSDSC1NB240G401 User Manual

IntelSSD DC S3500 Series Workload  
Characterization in RAID Configurations  
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Contents  
2.0  
3.0  
Supporting Documentation................................................................................... 5  
About This Guide .................................................................................................. 5  
6.3  
RAID 5 Performance Consistency...................................................................16  
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Tables  
Table 1  
Typical Mixed Workloads in Data Center Applications....................................... 7  
Figures  
Figure 1  
Figure 2  
Figure 3  
Figure 4  
Figure 5  
Figure 6  
Figure 7  
Figure 8  
Figure 9  
RAID 1 Random 100% Write @ 4KB Transfer Size with Average Latency............11  
RAID 1 Random 70% Read @ 4KB Transfer Size with Average Latency .............11  
RAID 1 Random 90% Read @ 4KB Transfer Size with Average Latency .............12  
RAID 1 Random 100% Read @ 4KB Transfer Size with Average Latency ...........12  
RAID 1 Maximum Latency for 2-drive and 8-drive Configurations ......................13  
RAID 5 Random 100% Write @ 4KB Transfer Size with Average Latency ...........15  
RAID 5 Random 70% Read @ 4KB Transfer Size with Average Latency .............15  
RAID 5 Random 90% Read @ 4KB Transfer Size with Average Latency .............16  
RAID 5 Random 100% Read @ 4KB Transfer Size with Average Latency ...........16  
Figure 10 RAID 5 Maximum Latency for 3-drive and 8-drive Configurations ......................17  
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1.0 Revision History  
Document  
Number  
Revision  
Number  
Description  
Revision Date  
December 2013  
Initial release  
329903  
001  
2.0 Supporting Documentation  
For more information on Intel SSDs, see the corresponding documentation.  
Document  
Document No./Location  
328860  
Intel® Solid-State Drive DC S3500 Series Product Specification  
3.0 About This Guide  
This guide describes Intel® SSD DC S3500 Series performance characteristics in RAID  
configurations across multiple workloads, and provides analysis to help optimize  
performance.  
The audience is technical IT professionals: Systems, Storage, Database, and Application  
Engineers.  
4.0 Overview  
The Intel SSD DC S3500 Series provides high random read and write storage  
Input/Output Operations per Second (IOPS) across mixed read and write workloads. This  
high random performance and the consistency of IOPS under workload deliver robust  
and scalable operation when used behind a RAID controller. Data centers can benefit in  
both performance and TCO by using the Intel SSD DC S3500 Series in the appropriate  
applications.  
Compared to the approximately 200-300 random IOPS that a single 15K SAS hard disk  
drive (HDD) can provide, an Intel SSD DC S3500 Series operates at much higher IOPS;  
up to 75,000 IOPS for random 4KB reads and up to 11,500 IOPS for random 4KB writes,  
over the entire span of the SSD. The Intel SSD performance numbers are based on the  
Intel product specification sheet, as derived from internal Intel testing. With real-world  
workloads, the IOPS that any particular device can produce will vary depending on  
several factors: the application’s ability to produce IOPS, the ratio of random to  
sequential access, the block transfer size, the queue depth, the read/write mix of the  
workload, and overall resource utilization in the server running the workload.  
This guide presents data for RAID 1 and RAID 5 configurations due to their prominence  
in the datacenter. Additional RAID levels are currently being tested and will be  
presented in future revisions, or as separate papers.  
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A selection of workloads that represent both best-case performance and real-world  
performance are presented in this white paper. These scenarios give the IT professional  
a better understanding of the capabilities of the Intel® SSD DC S3500 Series drive when  
used in conjunction with a hardware RAID controller. More importantly, it helps the IT  
professional understand a variety of workloads and circumstances in which Intel SSD  
technologies will accelerate those workloads and provide business value for their  
organization.  
4.1 What Impacts SSD IO Performance  
Although Intel SSDs excel in delivering random read and write IOPS, it is important to  
remember that more IO activity at the application level results in higher CPU utilization  
in the applications’ host. In addition to the abilities of the SSD, IO performance in any  
particular situation is dictated by how the particular application scales, and the IO profile  
of the workload produced by the application.  
The following workload-specific characteristics have a direct impact on the ability of the  
SSD to produce IO:  
Read/Write Mix – NAND programming (writes) and read timing (reads) differ  
significantly at the hardware level. Because of the higher controller overhead  
required for processing writes, the number of read IOPS are often higher than  
write IOPS. Real world workloads are most often a mix of read and write.  
Random/Sequential Mix – IOPS can vary depending on the ratio of sequential  
versus random accesses. With higher random write workloads, more data  
movement and greater data management activity occurs in the drive. As random  
write activity increases, the IOPS serviceable to the host typically decreases.  
Queue Depth - Higher queue depths typically allow the SSD to generate higher  
IOPS through concurrent processing of commands. However, as the queue size  
increases, latency will be negatively impacted.  
Random Transfer/Block Size - With a smaller transfer size, the SSD controller has  
to work harder to maintain the logical-to-physical address mappings. In addition,  
the smaller the transfer size, the larger the logical space needed for its mapping.  
Once logical space constraint is reached, background re-mapping will take place.  
These frequent events slow IOPS.  
Available Spare Area – A larger spare area directly impacts random write and  
mixed read/write performance by minimizing the frequency of reclaim activities  
and freeing up processor cycles to support more host read/write requests. You can  
increase the spare area by over-provisioning the SSD. See the Intel® High  
Performance SATA Solid-State Drive Over-Provisioning an Intel® SSD White Paper  
for more information.  
In summary, the following principles of storage are often true concerning queue depth,  
block size, randomness, and per-IO transactional latency:  
As queue depth increases, IOPS increase, and latency increases.  
As block size increases, throughput increases, and latency increases.  
As randomness increases, IOPS decreases, and latency increases.  
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4.2 Queue Depth and Latency  
Latency – The amount of time needed to service one outstanding IO to the drive,  
measured in milliseconds (ms) or, with SSDs, microseconds (µs).  
The Intel® SSD DC S3500 Series supports a maximum queue depth of 32 per drive. In a  
RAID array, the queue depth is multiplied by the number of drives in the RAID set.  
Example: In a RAID 5 set of 8 drives, the maximum total queue depth would be 256 (8  
X 32). As more commands are queued in the SSD, average latency is impacted. Our  
internal testing indicates that average latency increases sharply with queue depths  
beyond 8. However, these high queue depths can increase IOPS with read intensive  
workloads.  
Obtaining the best performance for a particular application requires balance. The  
challenge is to achieve high speed or IOPS at an acceptable latency level. This white  
paper presents lower queue depths of 1, 2, 4 and 8 per drive. The results shown  
demonstrate favorable speed and IOPS generation without pushing latency to extreme  
levels.  
4.3 Why Mixed Workload Is Important  
Mixed random workloads are predominant in data center and enterprise applications.  
Intel SSDs have been deployed in a variety of these applications ranging from content  
delivery and video on demand networks, to Internet datacenter portals and database  
management servers. Although these applications see unique IO traffic across the  
storage drive, there are commonalities in their usage of random and read/write mixed  
workloads.  
Table 1 shows an overview of transfer sizes, read/write mixes and randomness in  
commonly used workloads in data center applications. These are based on commonly  
available industry information and information available through such benchmarks as,  
TPC-C, TPC-E, TPC-H, and TPOX, which attempt to mimic these real world applications.  
Table 1.  
Typical Mixed Workloads in Data Center Applications  
Application  
Transfer Size  
4KB/8KB/16KB+  
4KB  
%Random  
~75%  
%Read  
~95%  
~70%  
~70%  
~95%  
~95%  
~95%  
~95%  
Web-Servers  
Exchange Email  
Database OLTP  
Decision Support  
Video On Demand  
Search Engine  
~95%  
~95%  
~95%  
~95%  
~95%  
~95%  
4KB/8KB  
16KB+  
16KB+  
4KB/8KB/16KB  
16KB+  
Cache  
Content Delivery Network  
16KB+  
~95%  
~70%-95%  
Based on these usage trends, small transfer sizes–ranging from 4KB to 16KB and  
above–are common in enterprise and data center applications. Also, much emphasis is  
placed on random accesses, and although there are varied levels of read and write  
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mixes, read-intensive workloads are more prominent. In summary, it is important to  
select the proper SSD for a particular workload.  
The examples presented here use 100% write and 100% read workloads to show the  
maximum performance in these areas. Also, 70%/30% read/write and 90%/10%  
read/write are used in order to simulate typical workloads in the datacenter.  
4.4 Drive Endurance  
Drive endurance, or wear, is an important consideration when selecting an SSD for a  
particular application. The Intel® SSD DC S3500 Series drive is a standard endurance,  
enterprise class drive, designed for read-heavy workloads. It is important to understand  
how drive wear is affected by the RAID level.  
A RAID level that uses dedicated parity, such as RAID 4, will write all parity to a single  
drive. This can potentially cause the parity drive to wear faster than the other drives in  
the set. Distributed parity RAID levels (RAID 5 and RAID 6) reduce this issue.  
RAID 1 and RAID 5, as tested in this example, shows very consistent wear across all  
drives in the RAID sets. This is due to the tests using the full LBA space of the RAID set,  
thereby not creating any hotspot activity.  
4.5 Selection of RAID Controller  
There are many quality RAID controllers on the market today, with varying levels of  
performance, features and price points. Below are the important features considered in  
selecting the RAID controller for this sample test:  
RAID levels available  
Controller chipset  
PCIe* version  
SAS/SATA speed  
Internal/External ports  
Compatibility with SSDs  
Within these categories, the LSI* MegaRAID 9265-8i was chosen for the following  
reasons:  
RAID 0, 1, 5, 6, 10, 50, 60 are supported  
LSISAS2208 Dual-Core RAID on Chip (ROC)  
1 GB 1333MHz DDR3 SDRAM Cache  
x8 PCIe 2.0  
6Gb/s per port  
8 internal SAS ports  
SSD support  
Relative availability/popularity in the industry  
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5.0 RAID 1  
5.1 Test System Specifications¹  
The system used for RAID 1 testing include the following:  
Intel® R2208GZ4GC-IDD 2U rack mount server  
Intel® S2600GZ server board  
2x Intel® Xeon® E5-2690 8-core CPUs (2.9 GHz)  
Intel® C602 chipset  
192GB DDR3-1333 memory  
Microsoft Windows Server 2008 R2*, 64-bit  
LSI MegaRAID 9265-8i* controller card  
2x up to 8x Intel® SSD DC S3500 Series 480GB drives  
BIOS configuration changes:  
Hyper-Threading disabled²  
RAID controller configuration:  
256KB Striping (default)  
No Read-Ahead³  
Write-Through³  
Direct I/O  
Windows Drive Configuration:  
Basic disk  
GUID partition table  
Simple volume  
Use full available space  
NTFS format  
Test Software configuration:  
IOMeter 2009.10.22  
1x worker per drive in RAID set  
Notes:  
1.  
The system was selected to make sure the performance of the RAID card and the SSDs would not  
be inhibited by the server.  
2.  
3.  
Hyper-Threading is disabled in this test system specifically due to additional latency introduced  
during benchmark testing. In any practical application, Hyper-Threading would NOT be disabled.  
In the configuration of the RAID set, No Read Ahead and Write-through are used due to the speed  
of the SSDs. Read and write caching was designed for use with HDDs. Caching with SSDs introduces  
additional overhead thus interfering with the SSDs performance.  
4.  
One thread, or worker, per drive was used in order to simulate the manner in which many  
applications utilize storage and also to attempt to saturate the communication channels to the SSDs.  
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5.2 Intel® SSD DC S3500 Series in RAID 1 Performance  
Characterization Data  
This section provides performance characterization data for the Intel® SSD DC S3500  
Series in RAID 1 configurations.  
To establish baseline expectations for IOPS, the Intel SSD DC S3500 Series 480GB  
drives were evaluated in RAID 1 sets of 2, 4, 6 & 8 drives. The data collected was based  
on a different mix of read and write random and sequential workloads. Since higher  
queue depths can sometimes yield higher IOPS, queue depths of 1, 2, 4, & 8 per drive  
were chosen in the test setup. Multiple transfer sizes were tested, however, only  
selected data is presented here. All tests were done using the entire LBA range of the  
virtual drive. Tests were repeated at least twice to validate results.  
Drives were prepared using IOMeter to fill the entire user area of the drive with data.  
Then, the first workload of each type (Sequential or Random) was 100% write  
performed for 120 minutes. Each subsequent workload was run for 12 minutes, with  
average IOPS collected over the last 10 minutes of the run.  
The following figures show the different levels of performance for a selection of  
configurations.  
Note: The scale of the IOPS charts is variable to clarify the changes that occur as drives are  
added.  
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Figure 1.  
RAID 1 Random 100% Write @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
Notes:  
Figure 1 - The write performance of the two drive RAID 1 set matches the write performance of a  
single Intel® DC S3500 drive. This indicates very low latency introduced by the RAID controller.  
As more drives are added, the write performance scales linearly. At four drives, the performance is  
2x that of a single drive, at six drives, it is 3x higher and at eight drives it is 4x. This is true at all  
queue depths tested and at transfer sizes from 4KB to 128KB. In this case, queue depth does not  
affect performance significantly.  
At a queue depth of 1, the average latency for 100% write at 4KB transfer size is less than 200 µs.  
Latency increases as the queue deepens, ending at 1.4ms for a queue of 8. It is interesting to note  
that latency is not affected by the number of drives.  
Figure 2.  
RAID 1 Random 70% Read @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
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Figure 3.  
RAID 1 Random 90% Read @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
Figure 4.  
RAID 1 Random 100% Read @ 4KB transfer size with  
Average Latency  
Intel internal testing, October 2013  
Notes:  
Figures 2, 3 - In mixed workloads, 70% read and 90% read, IOPS increase with additional drives  
and show slightly exponential growth with deeper queues.  
Figures 2, 3, 4 - Average latency for 70% read starts out similar to 100% write, but the progression  
is not as steep through deeper queues, ending between 500-600 µS. Average latency for 90% read  
and 100% read continue to improve due to the higher speed of reads over writes.  
Figures 2, 3, 4 - The latency of the two drive set is lower than other drive counts as read  
percentage increases due to the manner in which the LSI controller deals with the additional drives.  
This is expected behavior. For more information, please contact LSI for details.  
Figure 4 - At 100% read the IOPS performance scales linearly. In other words, the IOPS for four  
drives is double that of two drives, six drives is triple that of two drives, and eight drives is four  
times that of two drives.  
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5.3 RAID 1 Consistency  
Consistency behind a RAID controller is very important because the performance of any  
RAID set is limited by the lowest performing drive. As a RAID set increases in number of  
drives, the probability of any given drive performing poorly increases. Therefore, if the  
model of drive used is inconsistent in its performance, the inconsistency increases with  
the size of the RAID set.  
The Intel® SSD DC S3500 Series drive has shown excellent consistency when used as a  
single drive. Figure 5 illustrates the consistent of DC S3500 in RAID sets. Notice that the  
maximum latency is grouped very tightly for both the two-drive and eight-drive RAID  
sets, indicating there is very little change in consistency as more SSDs are added.  
Figure 5.  
RAID 1 Maximum Latency for 2-drive and 8-drive  
Configurations  
Intel internal testing, October 2013  
5.4 RAID 1 Performance Conclusions  
RAID 1 is a very good choice for data needing robust replication. The RAID controller  
used shows good bandwidth with low latency causing little to no effect on read and write  
speeds of the SSDs. The linear scaling of read and write performance with additional  
drives shows that adding more drives would provide good ROI in most applications. The  
highest throughput seen in this test was 2300 MB/s during 100% read using eight drives  
with transfer size of 128KB and a queue of 8 per drive. This means the theoretical  
bandwidth limit of the PCIe lanes was not reached (4000 MB/s for x8 PCIe 2.0). It is  
theoretically possible that more than eight drives could be used and obtain an increase  
in performance, depending on the latency introduced by the necessary SAS expander.  
The consistency of the drives is well demonstrated in these tests and shows that  
Intel SSD DC S3500 Series drives provide high performance with excellent stability,  
even behind a RAID controller.  
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6.0 RAID 5  
6.1 Test System Specifications  
The system used for RAID 5 testing was identical to the system used for RAID 1 testing  
except the following changes:  
2x Intel Xeon E5-2680 8-core CPUs (2.7 GHz)  
3x up to 8x Intel SSD DC S3500 Series 800GB drives  
Note:  
For this test, 800GB drives were used. The rated performance of the Intel SSD DC S3500  
Series drive in 800GB, 600GB, and 480GB capacities are nearly identical, per internal Intel testing.  
6.2 Intel SSD DC S3500 Series in RAID 5 Performance  
Characterization Data  
This section provides performance characterization data for the Intel SSD DC S3500  
Series in RAID 5 configurations.  
To establish baseline expectations for IOPS, the Intel SSD DC S3500 Series 800 GB  
drives were evaluated in RAID 5 sets of 3, 4, 5, 6, 7 and 8 drives. The data collected  
was based on a different mix of read and write random and sequential workloads. Since  
higher queue depths can sometimes yield higher IOPS, queue depths of 1, 2, 4, and 8  
per drive were used in the test setup. Multiple transfer sizes were tested, however, only  
selected data is presented here. All tests were done using the entire Logical Block  
Address (LBA) range of the virtual drive. Tests were repeated at least twice to validate  
results.  
Drives were prepared using IOMeter to fill the entire user area of the drive with data.  
Then, the first workload of each type (Sequential or Random) was 100% write  
performed for 120 minutes. Each subsequent workload was run for 12 minutes, with  
average IOPS collected over the final 10 minutes of the run.  
The following figures show different levels of performance for a selection of  
configurations.  
Note:  
The scale of the IOPS charts is variable in order to clearly show the change as drives are added.  
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Figure 6.  
RAID 5 Random 100% Write @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
NOTES: There are gains in write performance as drives are added to the RAID 5 set. The change at queue  
depth 1 from three drives to six drives is approximately 58% increase in IOPS. For eight drives,  
the change is 97% increase in IOPS over the three drive set.  
At a queue depth of 1, latency increases as more drives are added to the RAID set, most likely  
caused by the additional overhead of calculating parity and striping across more drives. This  
increases as the queue deepens.  
Figure 7.  
RAID 5 Random 70% Read @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
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Figure 8.  
RAID 5 Random 90% Read @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
Figure 9.  
RAID 5 Random 100% Read @ 4KB Transfer Size with  
Average Latency  
Intel internal testing, October 2013  
Notes:  
Figures 7, 8, 9 - As the workloads become more read intensive, there is a steady increase in  
performance both as drives are added and as the queue deepens.  
Figures 7, 8, 9 – As read percentage increases, the exponential increase in latency is not as  
prominent with deeper queues. This is due to the speed at which reads are performed.  
6.3 RAID 5 Consistency  
Consistency behind a RAID controller is very important because the performance of any  
RAID set is limited by the lowest performing drive. As the number of different drives in a  
RAID set increases, so does the likelihood of any given drive performing poorly.  
Therefore, if the model of drive used is inconsistent in its performance, the inconsistency  
increases with the size of the RAID set.  
The Intel® SSD DC S3500 Series drive has shown excellent consistency when used as a  
single drive. Figure 10 illustrates that the DC S3500 is also very consistent in RAID sets.  
The three-drive and eight-drive data shows the maximum latency is grouped very  
tightly; indicating that adding more drives would have little impact on consistency.  
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Figure 10. RAID 5 Maximum Latency for 3-drive and 8-drive  
Configurations  
Intel internal testing, October 2013  
6.4 RAID 5 Performance Conclusions  
The RAID 5 write performance data illustrates the additional processing power required  
of the RAID controller to calculate parity and stripe data across multiple drives. There is  
diminished performance gain be adding drives when compared to RAID 1. Intel’s data  
also shows that in mixed workloads and in pure reads, RAID 5 performs well, reaching  
over 300K IOPS in 100% read at a queue of 8 per drive on eight drives. As the  
workloads become more read heavy, latency drops from a high of 2.2 ms (100% write)  
to a low of 140 µs (100% read). The highest throughput achieved was 2400 MB/s with  
eight drives, 100% read, 128KB transfer size, and queue depth of 8. This leaves room  
for possible improvement by adding more drives to the RAID set.  
In configurations where RAID 5 would traditionally be used, SSDs would provide  
significant performance gain over HDDs. Additionally, RAID 5 with SSDs could be used in  
situations where RAID 5 with HDDs would not perform well.  
The consistency of the drives is well demonstrated in these tests and shows that  
Intel® SSD DC S3500 Series drives consistently offer higher performance with excellent  
stability, even behind a RAID controller.  
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7.0 Summary  
The Intel® SSD DC S3500 Series drive has proven itself in many applications where  
speed and reliability are essential. The data in this paper shows that this drive is very  
robust behind a RAID controller.  
In RAID 1 configurations, write performance is as expected for this setup; that is, a two  
drive set matches the single drive specification, and increases linearly as drives are  
added to the set. With eight drives at queue depth 1 per drive, this configuration  
processes over 50K write IOPS with 4KB blocks. The RAID controller adds very little  
latency, but latency does increase as the queue depth grows and, as more drives are  
added to the array. Read performance increases with additional drives and with queue  
depth, reaching over 200K read IOPS with eight drives, a queue of 8 per drive and 4KB  
blocks. More importantly, the performance on mixed workloads was excellent and  
increased as more drives were added. The 70% read workload topped out at close to  
110K IOPS with 4KB blocks, and the 90% went to nearly 150K IOPS with 4KB blocks  
(both at queue of 8 per drive). The highest throughput seen in this test was 2300 MB/s  
during 100% read using eight drives with transfer size of 128KB and a queue of 8 per  
drive. This means the bandwidth limit of the PCIe lanes was not reached (4000 MB/s for  
x8 PCIe 2.0). It is theoretically possible that more than eight drives could be used and  
an increase in performance obtained.  
In RAID 5 configurations, write operations increase both as drives are added and as the  
queue depth increases. The increase in write performance with queue depth is somewhat  
surprising and is most likely attributed to the RAID controller and the scaling effect of  
the cache in each drive. This may be due to the way the controller writes the stripes to  
the drive set, possibly consolidating the 4KB blocks into the 256KB stripes. Read  
performance is also very good, with eight drives reaching 300K IOPS with 4KB blocks  
and queue depth 8 per drive. Mixed workloads show very good performance with 70%  
read hitting 75K IOPS at queue of 8 per drive and 90% read coming in at almost 140K,  
both with 4KB blocks. Latency on all workloads is very manageable, although, as the  
queue depth increases, so does the latency. The graphs show that as queues grow,  
latency increases at an increasingly higher rate.  
To summarize:  
In both RAID 1 and RAID 5, the Intel SSD DC S3500 Series drive shows  
excellent scalability, performance, and consistency.  
Very little latency was introduced by the RAID controller in RAID 1. In RAID 5,  
the overhead and latency are slightly higher.  
In random, mixed read/write workloads, SSDs perform significantly (as much as  
100 times) better than HDDs in a similar situation.  
With this RAID controller, there is the possibility of greater performance by  
adding more than eight drives in both RAID 1 and RAID 5 configurations.  
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8.0 Appendix  
8.1 RAID Levels  
RAID (Redundant Array of Independent Disks), developed in 1988 to improve  
performance, reliability and scalability of hard disk storage systems has become a  
standard in datacenters because of these qualities. There are many types, or levels, of  
RAID.  
RAID 0 uses block level striping to span one or more drives. This does improve  
performance, and increases capacity when more than one drive is used. However, there  
is no fault tolerance, so failure of any one drive will cause full data loss.  
RAID 1, also called mirroring, writes data identically to two drives, producing a mirrored  
set. Reads can be serviced by either drive, and writes occur in unison on both drives. If  
one drive has a hardware failure, the data is protected in the mirrored copy. RAID 1  
requires two drives. Many modern RAID controllers support RAID 1 sets of more than  
two drives, however, the original specification was for only two. Because of the 50%  
overhead, RAID 1 is the most expensive RAID type.  
RAID 2 uses bit-level striping with dedicated Hamming-code parity. This is a theoretical  
model and not used in practice.  
RAID3 uses byte-level striping with dedicated parity. This level is not commonly used.  
RAID 4 uses block-level striping with dedicated parity. All parity data is on a single drive.  
I/O requests are handled in parallel, increasing performance.  
RAID 5 uses block-level striping with distributed parity. Data and parity are distributed  
among all drives and requires all but one drive to be present. RAID 5 requires at least  
three drives and can survive a single drive failure.  
RAID 6 uses block-level striping with double distributed parity. Identical to RAID 5 in the  
way it writes data, however, parity is written twice in different locations. RAID 6 can  
survive 2 drive failures; therefore it is often used for larger sets of drives.  
RAID levels can also be nested for improved performance or fault tolerance. RAID 10,  
0+1, 50 and 60 are common combinations.  
December 2013  
329903-001US  
White Paper  
19  
 
   

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