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Review: Samsung 845DC PRO SATA 400GB Enterprise SSD |
Welcome to Myce’s review of the Samsung 845DC PRO 400GB SATA
Enterprise SSD (hereafter referred to as the 845DC PRO).
Excitingly, the 845DC PRO uses Samsung’s new 3D V-NAND. How
will it perform? Read this review for an authoritative performance assessment (Spoiler
– a new 4K Random Write King takes the throne).
Market Positioning and Specification
Market Positioning
This is how Samsung positions the 845DC PRO –
Specification
Here is Samsung’s specification for the 845DC PRO –
3D V-NAND
Credit goes to my Myce colleague Wendy for this brief
introduction to 3D V-NAND -
It's no secret that Samsung has been working on a new
type of NAND, dispensing with the 'planar' arrangement and the 'charge pump
device' (CPD), by moving to a 3D vertical stacking cylindrical cell arrangement
(V-NAND) where the cells are stacked vertically, with up to 32 layers, allowing
a much higher density. In V-NAND, the CDP is also gone, being replaced by a
Charge Trap Flash (CTF). A CPD stores the charge in a conductor where
imperfections in the material can cause electrons to leak, and thus reduce NAND
endurance. A CTF stores the charge in the isolating layer, where leakage is not
a problem. A CTF also requires much less voltage to store the charge, so as an
added benefit, V-NAND requires much less energy to store the charge.
Moving to a vertical cell stacking arrangement rather
than the planar design also has a huge advantage. Because stacking cells
vertically takes up less space, it has allowed Samsung to take a step back in
the cell node size, so instead of shrinking the current 19nm node size, Samsung
has been able to use a larger node size, most likely around 30nm. Increasing
the node size means better endurance. Couple the new CTF method of storing the
charge with the increased node size, and Samsung estimates that V-NAND could
have as much as ten times the endurance of NAND based on the 19nm planar
design.
Another advantage of using a larger node size, is that
NAND page programming times are reduced substantially. Typically, 19nm planar
NAND takes around twice the time to program a NAND page when compared to 30nm
3D V-NAND. The end result is you get higher performance which is much more sustainable.
The 845DC PRO uses the world’s first 24 layer 3D V-NAND
technology.
Product Image
Here are some pictures of the 845DC PRO we tested –
Now let's head to the next page, to look at Myce’s
Enterprise Testing Methodology.....
Please click
here
to view or download a detailed introduction to Myce’s Enterprise Class Solid
State Storage (‘SSS’) Testing Methodology as a PDF.
Put briefly:
All testing is performed on an OakGate Technology test unit
We perform two sets of Performance Tests:
- A full set of the mandatory Storage Network Industry
Association’s (‘SNIA’) tests as specified in their Solid State Storage
Performance Test Specification Enterprise V1.0 – SNIA
SSS PTS Version 1.0. - A set of tests, known as the ‘Myce/OakGate Full
Characterisation Test Set’, that provides readers with a fuller
characterisation of the solution.
We also review other important factors such as Power
Consumption, Data Reliability and Failover features.
A word about SNIA testing – before striking a partnership
with OakGate Technology I spent some time researching how I might implement
SNIA testing using freely available tools such as IOMeter and FIO. I arrived
at the conclusion that whilst it was theoretically possible it was
impractical. The reason for this is as without the automation offered by a
test bench, such as the OakGate Unit, the only way to meet the SSS PTS
requirements is to run the maximum number of test cycles and then to manually
look back at the results to determine when/if steady state has been achieved in
the workload specific test cycle, and then harvest the data from the qualifying
Measurement Window. This means that the test runs would always take a maximum
elapsed time, and there would be a great deal of human effort required to
review, gather, and report upon the data. I empathise with, acknowledge, and
respect the efforts of other reviewers who endeavour to meet the SNIA’s
principles in their testing - I am privileged and thankful to be able to use a
superb test bench which automates the whole process and allows me to meet the
SNIA’s specification in full.
Before we move on, let’s remind ourselves of some basics –
When reviewing the performance of an SSS solution there are
three basic metrics that we look at:
1. IOPS – the number of
Input/Output Operations per Second
2. Bandwidth – the number of
bytes transferred per second (usually measured in Megabytes per second, ‘MB/s’)
3. Latency – the amount of time
each IO request will take to complete (usually, in the context of SSS
solutions, measured in Microseconds, which are millionths of a second).
It is true to say that IOPS and Bandwidth had all been
growing rapidly before the advent of SSS solutions, but Latency can only be significantly
decreased by eliminating mechanical devices, and thus Latency is the single
most important aspect that SSS solutions deliver to enhance performance.
Latency in a technical environment is synonymous with delay.
In the context of an SSS solution it is the amount of time between an IO
request being made, and when the request is serviced.
Bandwidth, also commonly referred to as ‘Throughput’, is the
amount of data that can be transferred from a storage device to a host, in a
given amount of time. In the context of SSS solutions it is typically measured
in Megabytes per second (MB/s).
A great enterprise SSS solution
offers an effective balance of all three metrics. High IOPS and Bandwidth is
simply not enough if Latency (the delay in an IO operation) is too high. As we
will see in the test results presented below, as Latency increases IOPS will
inevitably decrease.
Queue Depth is the average amount
of IO requests outstanding. If you are running an application and the Average
Queue Depth is one or higher and CPU utilisation is low, then the application’s
performance is most probably suffering from a ‘Storage Bottleneck’.
Another important factor to
remember is that SSS performance is influenced by previous workloads, not just
the current workload, and especially by what has previously been written to the
drive. As specified in the SNIA SSS PTS the goal of all good Enterprise level
testing is to provide consistent circumstances, so that results can be compared
fairly across different SSS solutions – it is for this reason that all of our
tests start with a purge of the drive, so that it starts in a ‘Fresh Out of the
Box’ (FOB) state. Most tests then have a pre-conditioning phase where the
drive is put into a ‘Steady State’ before the test phase begins. Put briefly, a
‘Steady State’ is achieved when the performance of the drive no longer varies
over time and settles into a consistent level of performance for the workload
in hand. You can find a detailed explanation of ‘Steady State’ and how it is
determined in the SNIA tests in our Enterprise Testing Methodology paper, which
can be viewed or downloaded as a PDF by clicking here.
For interest, here are some
generally accepted assumptions that differentiate the use and therefore the
approach to testing Enterprise/Server and Consumer/Client SSS solutions:
Enterprise/Server SSS
assumptions:
- The drive is always full
- The drive is being accessed 100% of the time (i.e. the
drive gets no idle time) - Failure is catastrophic for many users
- The Enterprise market chooses SSS solutions based on their
performance in steady state, and that steady state, full, and worst case
are not the same thing
Consumer/Client SSS
assumptions:
- The drive typically has less than 50% of its user space
occupied - The drive is accessed around 8 hours per day, 5 days per
week, and typically data is written far less frequently - Failure is catastrophic for a single user
- The consumer/client market generally chooses SSS solutions
based on their performance in the FOB state
Esther
Spanjer, Director, Enterprise Business Development EMEA at Sandisk, said, 'I am
happy to commend Myce for their high level of professionalism and cooperation
during the review process', Ms. Spanjer added, 'I wish them every success in
their partnership with OakGate Technology and their initiative to provide
authoritative performance reviews for the Enterprise Solid State Storage market'
Now let's head to the next page, to look at the results
of our SNIA IOPS (Input/Output Operations per Second) Test.....
IOPS performance will typically
vary greatly depending on the nature of the IO traffic, including the mixture
of Read and Write operations, and the mixture of Block Sizes (the size of the
IO operation’s data packet, also referred to as IO Size). This test is designed
to benchmark the IOPS performance profile for random IO operations for 56
different combinations of Read/Write mix % and Block Sizes when in a Steady
State, which are of interest to most users.
All of the SNIA’s test
specifications define a ‘required’ set of parameters that must be run for the
test and then allow the operator to elect to run additional tests with
different parameters of their choice. It is the mandatory test with the
required parameters that we run. Note that all of the mandatory tests must be
conducted with fully random data
As previously mentioned, a key
principle of SNIA testing is to provide a consistent basis for comparing
different solutions from different manufacturers.
Here are the results -
You can see here a visual confirmation that Steady State
Convergence was determined at the end of Round 5.
Here is a 3D and tabular presentation of the results. Users
can simply refer to the grid to obtain the R/W mix and Block Size value of
interest. For example, Online Transaction Processing applications
typically run at a Block Size of 8K and a Read/Write Mix of 65/35, and users
can quickly understand how the device might perform under Steady State for
these access characteristics.
You can see that the 4K 100% Read IOPS result is 92,033 and
that the 4K 100% Write IOPS result is a simply outstanding 50,812 (which both exceed
Samsung’s specification of 92,000 and 50,000, respectively)! To put this in
perspective this is 10,000 IOPS higher than the fastest SAS or SATA drive we
have tested prior to this, which was the original Smart Optimus SAS 400GB drive
at 40,323.
Product Comparison
For interest we present a comparison of the 4K 100% Writes
and Reads results with those of the other Enterprise SSDs we have tested -
A new King of 4K Random Writes has taken the throne!
Now let's head to the next page, where we look at the
results of the SNIA Write Saturation Test.....
The objective of this test is
to observe the time evolution of the drive’s performance, as a function of
time, from a ‘factory fresh’, ‘fresh out of the box’ (‘FOB’) state. When a drive
is in a FOB state (e.g. after it has been purged by, for example by a SATA
Secure Erase or SCSI Format), we can expect an initial period of time when
writes can easily be accommodated by clean/empty blocks, but once all of the clean
blocks have been written to once and the drive’s controller must first clean
blocks (with erase write operations) before it can write new data, then we can
expect a slow down. The slow-down is usually quite dramatic and is commonly
referred to as the ‘write cliff’.
The Write Saturation Test is
easy to run as it requires no steady state determination – it can be easily run
in freely available software, such as IOMeter.
Here are the results -
You can see here a gradual drop in Write IOPS performance as
the 845DC PRO ECO reaches a Steady State. The fall, that begins at around Round
27, occurs when all of the available NAND has been written to once and the
drive must clean blocks on the fly, in preparation for accommodating further
writes – this is commonly referred to as the ‘Write Cliff’.
Note that the test was halted, as specified in the SNIA SSS
PTS, when 4 x the User Capacity had been written to the drive. You can see that
the 845DC PRO is settling into a steady state at around the 53,000 IOPS level,
which is excellent.
ust over
You can also see that the latency graph line is a mirror
image of the IOPS graph line.
Now let's head to the next page, to look at the SNIA
Throughput Test.....
The test is designed to measure the sequential Read and
Write IO performance for two Block Sizes, when under Steady State conditions.
One can easily compare the results produced by this test with box-top numbers,
which are usually stated as “Up to xxx MB/S”.
Here are the results -
You can see here that Steady State was achieved for both
Write IO sizes by the end of Round 5.
-
You can see here that Steady State for both Read IO sizes
was achieved by the end of Round 6.
Here are the average values recorded in the measurement
window –
Product Comparison
For interest we present a comparison of the 1024K sequential
reads and writes (single port) performance in comparison with those of the
other Enterprise SSDs we have tested -
Now let's head to the next page, to look at the results
of the SNIA Latency Test.....
The Latency Test measures average and maximum response times
using random IOs at specified Block Sizes and Read/Write mixes, taken under
steady state conditions. The test runs at a Queue Depth of 1 (1 outstanding
IO), thus the results give the baseline response time for a single IO request.
The test also reports maximum latency values, which can be
helpful to see if there might be processes within the drive that may cause max
Latency values to become larger.
Here are the results -
You can see here that Steady State Convergence was achieved
at the end of Round 5.
These are the Average and Maximum Latency Values observed in
the Measurement Window (measured in Milliseconds).
Here is a 3D graph showing, at a glance, the Maximum Latency
values for each combination of Read/Write Mix and IO Size.
Here is a 3D graph showing, at a glance, the Average Latency
values for each combination of Read/Write Mix and IO Size. These are excellent
results.
Product Comparison
For interest we present a comparison of the 4K 65% Reads 35%
Writes latency results in comparison with those of the other Enterprise SSDs we
have tested -
Now let's head to the next page, to look at the results
for the Myce/OakGate 4K Read and Write Latency Tests......
These tests steadily increase the random 4K IO demand in
terms of IOPS, and report the drive's response in terms of Average IOPS, Average
Latency and Maximum Latency. It is designed to show a drive’s maximum IOPS
capability and report the all important Latency numbers for each level of IOPS
demanded. The Maximum latency numbers give us an insight into the occurrence
of Latency peaks that could cause an unexpected response from time to time.
Here are the results –
Firstly, here is a graph showing the result for the initial
Pre-Conditioning step (4K Random Writes) –
4K Latency Read Test
You can see that the drive can no longer meet the increase
in IOPS demand at 94,000 IOPS, which is exceeding Samsung’s specification of 92,000.
You can see a gradual increase in read latency up to the
maximum IOPS mark. The Read Latency results are excellent.
You can see that there are a few max latency spikes.
Let’s have a close look at the distribution of the Latency
results at the 56,000 IOPS level (at one of the spikes) –
As this is the first time in this review, that we are
looking at a High Resolution Latency Histogram, here’s an explanation – The X
axis to the left is the count of the IOs in the observation period (in a Round)
that had a Latency of the value along the Y axis (please note that the X axis
is logarithmic to allow the low order counts of the huge number of IOs that
have been measured to be visible); the Y axis is the Latency value measured in
Microseconds; The X axis to the right is the % of the Total IOs observed that
have a Latency <= to a given Latency value; the rate of getting to 100% is
highlighted by the red graph line.
You can see that 99.9% of the Latency values are <= 210
Microseconds and there are relatively few outliers, so the quality of service
is excellent.
4K Latency Write Test
You can see here that the 845DC PRO starts failing to meet
the increase in IOPS demand at around 50,000. This is an excellent result,
which is spot on with regard to Samsung’s specification.
Here we can see that Average Write Latency stays below 75 microseconds
until a demand of 50,000 IOPS.
The maximum write latency results are more ‘spiky’ than
those for reads, but this is typical.
Now let’s have a look at the distribution of the Latency
Values at the 45,000 IOPS Mark –
You can see that 95% of the Latency Values are <= 270
microseconds. This is an excellent result.
Now let's head to the next page, to look at the results
for the Myce/Oakgate Reads and Writes Tests.....
The tests are designed to show the Random and Sequential,
Read and Write, performance metrics for different combinations of Queue Depth
and IO size.
Here are the results -
Random Reads
Random Writes
Here you can see a distinctive and healthy IOPS peak for the
4K IO Size.
Sequential Reads
Sequential Writes
Now let's head to the next page, to look at the results
for the Myce/Oakgate 4K Mixed Reads/Writes Tests.....
This test is designed to show the performance metrics for
different combinations of Queue Depth and Read/Write mix (the % of Reads and
the % of Writes making up the IO traffic)
4K Mixed R/W Test
You can see that there is no dramatic decrease in Read IOPS
as a small % of writes enters the mix.
Now let's head to the next page, to look at the results
of the Myce/OakGate Entropy Tests.....
These tests are designed to show performance metrics for
different combinations of Queue Depth and Entropy % (Entropy % is the degree to
which the data that is random and therefore incompressible). Testing with
different Entropy % levels has become important with the advent of controllers,
such as those from LSI Sandforce, that compress data before writing it to NAND.
Controllers that compress data can be expected to perform better with highly
compressible data (i.e. data with low Entropy).
The first test performs 5 minutes of Random 4K writes for
each combination of Queue Depth and Entropy %.
The second test does the same thing for a mixture of Read
and Write traffic (70% Reads, 30% Writes).
4K Entropy Write Test
You can see there is little or no variance in performance to
be found in any of the Entropy tests, as the degree of random data increases
(and this comment applies to all of the test results for the Myce/OakGate
Entropy Tests). We can therefore conclude that the 845DC PRO does not compress
data.
4K Entropy 70%_Reads_30%_Writes Test
As we saw no evidence of compression in the 4K Entropy Write
Test we skip the presentation of the 70/30 entropy results.
Now let's head to the next page, to look at Power
Consumption and Data Reliability.....
Power Consumption
I believe most people know that data centres are already one
of the major consumers of electricity in the industrialised world; indeed it is
estimated that currently 2% of all electricity consumption goes into IT
applications. According to the European Union the energy consumption of data
centres was 46 Terawatt hours in 2006 and is set to rise to 93 TW hrs by 2020. This
is equivalent to one hundred million 100W light bulbs burning 24 hours a day,
365 days a year.
Typically 40% of the power consumed by data centres is for
the IT load and 35% is for cooling the system. Generally speaking, if a drive
consumes more power it will produce more heat – so power consumption is indeed
a double edged sword. It is no surprise then that a significant proportion of
a data centre’s power consumption goes on servers. I understand cloud based
applications, such as Facebook, are the primary cause of the growth in servers
and the demand for storage space.
If you are a Facebook user, like me and the Reynolds sibs, and
you reside in Europe – this is most probably where your data is click here. Some
interesting Facebook statistics – Facebook has more than 1 Billion monthly
active users, it generates 1 Trillion page views per month and more than 219
Billion photos have been uploaded since launch – amazing! Here is an
interesting video showing the remarkable scale of Facebook’s largest North
American data centre click
here.
My thanks to Anna of Intel for pointing me to the following
Info-graphs -
The following graph uses the typical Power Consumption, when
active, as published in the respective manufacturer’s specification. The value
for the Kingston E100 is calculated as the average of 1.2W (TYP) Read and 2.7W
(TYP) Write.
The 845DC PRO has excellent power consumption
characteristics.
Data Reliability
The 'Unrecoverable Bit Error
Rate' (UBER),as defined by JEDEC, the global leader in developing open
standards for the microelectronic industry, is a metric for data corruption
rate equal to the number of data errors per bit read after applying any
specified error correction method. UBER = number of data errors / number of
bits read. JDEC specifies that the maximum error rate allowable for an
Enterprise level SSS solution is one error in every 10^16 bits read.
