1 Jan, 2009

Solid State Drives vs Hard disk drives

Posted by

Intro

  • A solid state drive stores its data in solid-state memory (Flash / SRAM / DRAM)
  • Flash does not require constant power and is non-volatile while SRAM and DRAM are volatile

Speeds

  • Flash maybe slower than even tradition HDDs on big file access
  • Flash is considerably slower than conventional disks for small writes. This is partly due to their large erase block size of 0.5-1 MB
  • SSDs are faster than HDDs for small random reads due to negligible seek time (no moving parts)
  • Check the comparison table at http://www.storagesearch.com/ssd-ram-v-flash.html.  When Flash based SSDs are used for equal reads and writes they are actually slower than HDDs. However if small random reads far outweigh writes, the performance gains can be upto 100x!!?
  • Download the paper – Comparison of Drive Technologies for High-Transaction Databases. Findings below -
    • HDDs: Small reads – 175 iops/s, Small writes – 280 iops/s
    • Flash SSDs: Small reads – 1075 iops/s (6x), Small writes – 21 iops/s (0.1x)
    • DRAM SSDs: Small reads – 4091 iops/s (23x), Small writes – 4184 iops/s (14x)
  • Another whitepaper on Flash vs HDDs is Understanding Flash SSD Performance. Findings below -
    • Read performance: Flash outperforms hdds by a large magnitude for small block size
    • It is with write performance that Flash SSDs become problematic. The issue here is the internal structure used within the Flash storage array. This structure includes a collection of bytes called an “erase block”. When you write to a Flash SSD, the drive itself cannot just update the sectors you are changing, but must merge your changes with existing data to update a complete erase block. As Flash SSDs have gotten faster and larger, erase blocks have grown as well. Flash erase blocks used to be 16K in length. Now they are 1 Megabyte for small SSDs extending up to as large as 4 Megabytes for some models.
    • If you are doing pure reads, a Flash SSD will typically be 20x faster than a hard disk for small random reads. If you are doing pure random writes, the same drive might be 15x slower than a hard disk
    • Of pertinence is the table which shows how a small % of writes can destroy Flash SSD Performance. It is for this reason alone that Flash SSDs, by themselves, are not very effective with random update applications like on-line databases, mail queues, and other environments that involve a lot of small updates
  • One can improve write performance of a Flash SSD using the following methods -
    • OS Write caching – OS buffers writes which eventually get written to disk making the writes appear faster
    • File systems optimized to minimize random writes – YAFFS, JFFS2.
    • Managed Flash Technology – a patent pending technology by easyco which enables Flash Drives to write clusters of random data in linear streams

Costs

  • As of mid-2008, SSD prices are still considerably higher per gigabyte than are comparable conventional hard drives: consumer grade drives are typically US$2.00 to US$3.45 per GB for flash drives and over US$80.00 per GB for RAM-based compared to about US$0.12 per gigabyte for hard drives
  • DRAM based SSD require more power than hard disks when operating, and need continuous power when not in use if the data needs to be persistent
  • Check article Flash vs DRAM Price Projections – for SSD Buyers
    • In the first half of 2007 the difference in user price between a RAM versus Flash SSD was about 45 to 1. A year later in the first half of 2008 that ratio had changed to 25 to 1
    • However NAND has been on a steeper price decline than DRAM for its entire existence. The price of a gigabyte of DRAM declines (on average) 32% per year. There are indications that this decline may slow. Meanwhile, NAND’s price per gigabyte declines faster, at an average of 50% per year

My Conclusions

  • DRAM based SSDs are crazy expensive. They serve best for volatile caches (eg, memcached pools etc). If you have servers dedicated to serve in-memory cache data, it may reduce your cost to add DRAM SSDs to these clusters since they are likely not going to bottle-neck on CPU anyways
  • Flash based SSDs would work in an environment where the % of writes is low. As can be seen in some of the above benchmarks, a flash based SSD starts degrading in performance in comparison to HDDs in environments with just 5% writes. If one wants to use Flash based SSDs in environments with substantial writes, one should use special filesystems (YAFFS / JFFS2)  and/or use Managed Flash Technology
  • Flash based SSDs work like a charm in a read-only or mostly read environment
Tags: , , , , , ,
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by sanjay on January 25, 2009 @ 10:07 am
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by sanjay on January 25, 2009 @ 10:07 am
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by Bhavin on January 29, 2009 @ 12:07 am
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by Dushyanth on February 12, 2009 @ 9:42 am
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by james braselton on April 6, 2009 @ 8:10 pm
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
comment_type == "trackback" || $comment->comment_type == "pingback" || ereg("", $comment->comment_content) || ereg("", $comment->comment_content)) { ?>

Trackbacks & Pingbacks
  • Comment by yangyang on March 25, 2010 @ 7:45 am

Comments
comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
George Moschovitis
January 11, 2009

Interesting data, I thought SSDs where an all-win proposition…

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
saurav
January 12, 2009

Went through your linkedin Profile- never expected you to be so tech savvy :) .

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
saurav
January 12, 2009

I would wish to connect with you, so would request your contact info :)

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
sanjay
January 25, 2009

It’s a superb article.

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
sanjay
January 25, 2009

Its superb.

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
Bhavin
January 29, 2009

thanks a lot saurav. U can drop a line to me at bhavin DOT t AT directi.com

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
Dushyanth
February 12, 2009

http://www.c0t0d0s0.org/archives/4832-SSD-at-Sun.html
A nice presentation about SSDs & traditional disks and interesting SSD usage scenarios. An important point this article points out is the lack of advances in rotational HDD’s performance & technology!!

Also check out Linus’s take on SSD’s for consumer grade usage – http://torvalds-family.blogspot.com/2008/10/so-i-got-one-of-new-intel-ssds.html

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
james braselton
April 6, 2009

HI THERE WITH THAT PERFORMANCE DATA IT SHOWS SSD OUT PERFORMED 15,000 RPM HARD DRIVES I HAVE NO IDEAR IF WESTERN DIGITAL WILL RELEASE THERE PROTOTYPE 20,000 RAPTOR OR IF HARD DRIVE COMPANIES WILL RELEASE A LASER HARD DRIVE AT 100 TREABYTES PER SECOND TOO IF HARD DRIVE COMPANIES WANT TOO TAKE MARKET BACK FROM FLASH MEMORY AND SOLID STATE FLASH DRIVE HARD DRIVE COMPANIES SHOULD PUT OUT THERE FASTEST HARD DRIVE AVALIBAL EXPECAILY FOR THE HARD CORE GAMERS WANTING 3 OR 4 RAPTORS IN THERE X-BOX OR PS3

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
Solid state hard drives
January 18, 2010

I’d love to see SSDs in Think Pads, if they get to the point there’s a good speed gain and weight savings–but realistically, since I have the better part of my 80GB drive full now there’s no way I’d buy one until 128GB SSDs get to be cheap, which I’m sure is years away still.

comment_type != "trackback" && $comment->comment_type != "pingback" && !ereg("", $comment->comment_content) && !ereg("", $comment->comment_content)) { ?>
yangyang
March 25, 2010

Rosetta Stone Spanish (Latin America) Level 1 with Audio Companion. I have used this popular Spanish rosetta stone software to learn Spanish with mix results.Our “TopTenREVIEWS Bronze Award” went to Rosetta stone french, a recognized leader in the language learning industry. Note for Intel Macintosh Users: rosetta stone V3 application for Macintosh is a universal application that will run natively on Intel Macs.Learn French in your own time and have fun.

Leave a comment

(required)

(required)

Spam protection by WP Captcha-Free