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The SSD Workload Performance Analysis

The SSD Workload Performance Analysis
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The performance qualities of flash-based solid state drives--so-called flash SSDs--have been disputed all over the Web. While the peak performance numbers of the latest products are typically more than impressive (featuring throughput levels of almost 250 MB/s and up to several thousand I/O operations per second), real-life performance may be very different. In fact, over time, performance can even come down to levels at which conventional hard drives are faster due to their steady performance.

Today's SSDs simultaneously benefit and suffer from flash technology. But if you leave all the poor performers aside, the latest generation offerings from Intel and Samsung definitely show more potential than shortcomings.

What is Performance?

Compared to flash SSDs, the performance evaluation of hard drives has been rather simple: you want to know the throughput performance in megabytes per second, and access time in milliseconds, for both desktop and notebook drives. Sometimes you need to add I/O performance analysis for servers and workstation products before making a decision. Although power efficiency is becoming more and more important, those are the performance metrics that matter most.

Application benchmarks help to assess performance in real life environments by simulating representative operational sequences. The hard drive format (3.5”/2.5”), recording technology, data density, and spindle speed have been the key parameters that historically had most influence on performance. Apart from them, the remaining factors, such as the interface bandwidth or cache size, are secondary.

Flash SSDs are Different

Essentially, hard drives are best at reading or writing data sequentially—the more they have to reposition their heads to tackle random operations, the more they slow down in terms of both throughput and I/O operations per second.

This is where flash SSDs kick in: they have extremely quick access times, as they just have to pick the right position within the memory array instead of moving physical components. In addition, the latest products are capable of delivering roughly twice the maximum throughput of a conventional hard drive, by lining up flash memory in multiple channels similar to dual-/triple-channel RAM configurations or RAID technology. The analysis of I/O performance reveals the degree of intelligence of the flash controller used in a flash SSD, as they have to maximize performance while providing wear-leveling for the flash cells.

The Black Box

As flash SSDs have become more complex, they have also become veritable “black boxes.” The physical location and strategy for storing data isn’t as simple as it is on hard drives, where it is rather easy to imagine how data is stored. By looking at the type of NAND flash memory, you can estimate whether a flash SSD will just be good at sequential reads, or if it can deliver high write and I/O performance as well. Single-level cell (SLC) flash, is the faster type; it stores one chunk of information per segment, making it quick. But SLC is expensive--often too expensive even for mainstream devices. Multi-level cell (MLC) flash is the increasingly popular alternative; it stores multiple information units per flash segment using several voltage levels, providing higher capacities.

However, the combination of smart controllers and multiple flash channels results in erratic use of the available resources. This means that a sequential stream of data is never actually written sequentially. The fact that files can be anywhere between a few bytes and many gigabytes, and that data is typically written, read, erased, and written again adds a layer of complexity that can have a substantial impact on flash SSD performance. This can become even more pronounced once you utilize the entire SSD capacity, leaving fewer options for the flash controller to optimize performance. Luckily, there are precautions you can take and firmware updates available as well. These updates continually improve flash controllers to reduce performance fluctuations, allowing future operating systems to catch up and work with new file systems that are aware of the characteristics of storage products.

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  • 1 Hide
    mrubermonkey , April 27, 2009 7:16 AM
    Props to you guys for this review.
  • 3 Hide
    Tindytim , April 27, 2009 7:47 AM
    I really wish we were able to Thumb up or Thumb down articles. This one would get a large thumbs up from me.
  • 1 Hide
    chookman , April 27, 2009 7:58 AM
    Thumbs up on this one too from me. Although if anyone desires more in depth understanding of the problem i found the PC Perspective articles better in that aspect.

    Intel Firmware change
    http://www.pcper.com/article.php?aid=691

    OCZ Indilinx Chip
    http://www.pcper.com/article.php?aid=670
  • -9 Hide
    chookman , April 27, 2009 7:58 AM
    Thumbs up on this one too from me. Although if anyone desires more in depth understanding of the problem i found the PC Perspective articles better in that aspect.

    Intel Firmware change
    http://www.pcper.com/article.php?aid=691

    OCZ Indilinx Chip
    http://www.pcper.com/article.php?aid=670
  • -8 Hide
    chookman , April 27, 2009 7:59 AM
    Thumbs up on this one too from me. Although if anyone desires more in depth understanding of the problem i found the PC Perspective articles better in that aspect.

    Intel Firmware change
    http://www.pcper.com/article.php?aid=691

    OCZ Indilinx Chip
    http://www.pcper.com/article.php?aid=670
  • 5 Hide
    empstar , April 27, 2009 8:55 AM
    why don't show the HDD read / write data here together with SDD?
  • -4 Hide
    lire210 , April 27, 2009 10:56 AM
    this will not matter at all to servers until the price gooes down. the speed does not make sence in the 4+ bucks a gig. normal hd are safer just in the fact that you can put 7 hd and put it in a raid one fails o well. plus 800 bucks for 64gb o my god
  • 4 Hide
    snotling , April 27, 2009 11:29 AM
    lire210this will not matter at all to servers until the price gooes down. the speed does not make sence in the 4+ bucks a gig. normal hd are safer just in the fact that you can put 7 hd and put it in a raid one fails o well. plus 800 bucks for 64gb o my god

    Servers are actually where these drives makes the most sense, and you can RAID SSDs just like you RAID HDs... and about being "safe" well I would put my money on the technology with no moving parts!
  • 6 Hide
    xsamitt , April 27, 2009 12:27 PM
    I keep waiting for a reviews of new monitors.it seems we keep getting almost the same kind of topic every week lately.
  • 0 Hide
    rubix_1011 , April 27, 2009 1:37 PM
    I have to agree with most people on this one...a flashback to the really good reviews Tom's did in the past. A very relevant review for most people with some good data and testing steps.
  • 0 Hide
    arkadi , April 27, 2009 1:39 PM
    Well it like it was written specially for me. Grate job! One of the best articles i encounter in long time.
    I posted a question on storage configuration just few day ago, with no reply btw, with exactly the same thing on my mind. Hope we can go deeper with that, and talk how we can take an advantage of what we learned here in different situations with diffident storage/system configuration's, combining SSD with regular drives, raid configurations, moving tmp/swap some programs etc.. to different drives etc...
  • -4 Hide
    arkadi , April 27, 2009 1:40 PM
    Well it like it was written specially for me. Grate job! One of the best articles i encounter in long time.
    I posted a question on storage configuration just few day ago, with no reply btw, with exactly the same thing on my mind. Hope we can go deeper with that, and talk how we can take an advantage of what we learned here in different situations with diffident storage/system configuration's, combining SSD with regular drives, raid configurations, moving tmp/swap some programs etc.. to different drives etc...
  • 1 Hide
    tipoo , April 27, 2009 1:45 PM
    Nice review. So will you guys be reviewing the 1TB PCI-Express OCZ SSD? :-)
  • 0 Hide
    Anonymous , April 27, 2009 2:50 PM
    So if your SSD starts to slow down, does a reformat get rid of that issue?
  • 0 Hide
    yourhighness , April 27, 2009 4:22 PM
    You guys had any problems with that Power Supply?

    I bought an OCZ Elite Extreme 800W PSU last year an dhad 3 of them die in 6 months....The RMA process was long and slow, but they eventually made it right by upgrading me to a PC Power and cooling PSU.
  • 2 Hide
    Area51 , April 27, 2009 4:49 PM
    lire210this will not matter at all to servers until the price gooes down. the speed does not make sence in the 4+ bucks a gig. normal hd are safer just in the fact that you can put 7 hd and put it in a raid one fails o well. plus 800 bucks for 64gb o my god

    You need to have a better understanding of the problem before you make statements like this...

    1. The number of HD required to get the same IOPS will put the total price to be higher than SSD's
    2. The power requirement is much higher for the number of HD that you need to get the same performance as a single Intel SLC SSD. This can drop the power consumption of a server significantly down from regular HD, and increase it’s performance.
    3. Remember that in many servers it’s not the capacity that matters, It’s the performance that is more important.
    4. Since SSD's can do a very nice job of simultaneous read, and write running multiple jobs is not derogated by the SSD's as it is with regular HD's.
    5. SMART command in SSD’s can give you a predictive failure analysis, something that you cannot do with HD’s, HD’s can only show you if the Drive is good or bad. This is very important since data can be copied before the drive goes bad.
    6. MTBF of SSD’s (at lease Intel’s) are much higher than HD’s. 2M hrs. vs 1.2M hrs on HD’s


  • 2 Hide
    krazyderek , April 27, 2009 11:06 PM
    wheres the OCZ vertex ?????
  • 0 Hide
    krazyderek , April 27, 2009 11:08 PM
    lire210this will not matter at all to servers until the price gooes down. the speed does not make sence in the 4+ bucks a gig. normal hd are safer just in the fact that you can put 7 hd and put it in a raid one fails o well. plus 800 bucks for 64gb o my god

    have you seen how much SAS drives are??
  • 0 Hide
    hustler539 , April 28, 2009 11:07 AM
    Good to see more review sites doing articles on these performance degradations, helps us make a better informed decision when purchasing new hardware.

    Here's another great article which gives you a good in depth look at it
    http://www.anandtech.com/storage/showdoc.aspx?i=3531&p=4
    a must read if you are thinking of upgrading to some of those new shiny ssds
  • -1 Hide
    hustler539 , April 28, 2009 11:08 AM
    krazyderekwheres the OCZ vertex ?????



    ^ a review of that is in the article as well
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