The SSD Guy has been asked a number of questions lately about SSDs and RAID. Most of these center around the difference in failure behaviors between SSDs and HDDs – HDDs fail randomly (if ever), while SSDs fail relatively predictably due to wear.
Oddly enough, SSD failures due to wear make them a little friendlier than HDDs. The wear mechanism is managed by the controller in the SSD. SSDs have spare blocks, and the controller manages those blocks, so the controller understands exactly how much wear the SSD has undergone and how much room is left before the SSD will start to have difficulties. Continue reading “SSDs and RAID”
One of the thorniest issues in SSD design how to manage erasing blocks that are no longer in use. That’s saying a lot, because NAND flash presents so very many difficult challenges like wear leveling, bad block management, error correction, and write amplification.
The difficulty stems from the fact that all of today’s software was written for HDDs which don’t behave like the flash in an SSD. An HDD can over-write existing data with new data. In a flash SSD, a block must be erased before being over-written and this can take a half a second – a huge amount of time in the world of computing. Since the software doesn’t accommodate flash’s “erase-before-write” needs, the controller inside the SSD must take care of this bit of housekeeping. Unused and unerased blocks are moved out of the way and erased in the background. This is called the “garbage collection” process. Continue reading “SSD Garbage Collection”
The SSD Guy attended TechTarget‘s Storage Decisions Conference last week in San Francisco. Dennis Martin of Demartek gave a very good presentation called Making the Case for Solid-State Storage.
Demartek tests a lot of systems based on various forms of storage.
I really liked an expression that Mr. Martin shared to compare SSDs to HDDs. He said that SSDs cost dollars per gigabyte and pennies per IOPS, while HDDs cost pennies per gigabyte and dollars per IOPS. This is a really good way to think about the strengths and weaknesses of these two technologies. There is every reason to use a mix of both. Continue reading “Sometimes SSDs Don’t Improve System Speed”
An article in the Storage Newsletter caught The SSD Guy’s eye when it ran in July. The article consisted of a press release followed by an editorial comment:
While hard drives still have the cost advantage, it appears it’s becoming akin to sticking with a horse-drawn buggy in an age of automobiles by arguing that the upfront cost for a car is so much more than the cost of a horse. At some point, it just doesn’t make sense to ride a horse. How soon until the IT world gets there?
Continue reading “Are HDDs Obsolete?”
SSDs vary widely in performance. This is something that becomes amazingly clear when a number of these devices are put through a battery of tests.
Calypso Systems ran the SNIA SSD Performance Test Specification (PTS), outlined in an earlier post in this blog, on seventeen SSDs and a single HDD. The results appear, in miniature, in the graphic for this post. Continue reading “Not all SSDs are Created Equal”
The SSD Guy often hears people ask: “When will SSD prices drop below the prices of HDDs?”
This makes a lot of sense. After all, NAND flash, which makes up the bulk of the cost of an SSD is renowned for its rapidly-falling prices.
The short answer to this question is: “Never!” Continue reading “When will SSD Prices Drop Below HDD Prices?”
At Oracle’s October OpenWorld conference in San Francisco more exhibit hall space was dedicated to SSDs this year than ever before. That’s because Oracle runs faster on systems with SSDs than on systems without.
Even Oracle ships SSDs in its popular Exadata system, and the company recently announced that it had shipped over 1,000 installations since its introduction in 2009. Continue reading “SSD Presence Growing at Oracle OpenWorld”
Few realize just how long SSDs have been around. In fact, Dataram introduced the Bulk Core SSD in 1976.
This 2-megabyte wonder, introduced in 1976, was said to offer speeds 10,000 times those of a fixed-head disk, while reducing power consumption, with no moving parts much like the SSDs of today.
Some may object to my calling this an SSD – and with good reason. It didn’t use semiconductor memory technology, it used core memory. Continue reading “The First SSD”
On Tuesday, November 1, Seagate announced improvements to its flagship Barracuda line of 3.5″ HDDs for the desktop.
- The 5,900 RPM Barracuda Green will be discontinued in February
- The 7,200 RPM Barracuda XT will be re-named the Barracuda (without the XT designation, which indicates a “top of the line” speed)
- A new Barracuda XT line will be introduced at a later date and it will incorporate the hybrid design Seagate pioneered in the popular Momentus XT.
Capacities will range from 250GB-3TB. Continue reading “Seagate’s Barracuda to Add Hybrids”
A colleague – Isilon’s Rob Peglar – pointed out an interesting paper written by researchers at the University of Toronto in collaboration with Microsoft. The paper makes a case for using an HDD to cache writes to an SSD to improve storage system performance.
“Wait a minute!” you say. “An HDD as a cache for an SSD? This can’t be possible!” Continue reading “An HDD Cache for an SSD?”