A couple of specifications for SSD endurance are in common use today: Terabytes Written (TBW) and Drive Writes Per Day (DWPD). Both are different ways to express the same thing. It seems that one vendor will specify endurance using TBW, while another will specify DWPD. How do you compare the two?
First, some definitions. “Terabytes Written” is the total amount of data that can be written into an SSD before it is likely to fail. “Drive Writes Per Day” tells how many times you can overwrite the entire capacity of the SSD every single day of its usable life without failure during the warranty period. Since both of these are guaranteed specifications, then your drive is most likely to last a lot longer than the number given by the SSD’s maker.
To convert between the two you must know the disk’s capacity and the warranty period. If drive maker gives you TBW but you want to know DWPD you would approach it Continue reading
From time to time IT managers ask The SSD Guy if there’s an easy way to compare SSDs made with MLC flash against those made using eMLC flash. Most folks understand that eMLC flash is a less costly alternative to SLC flash, both of which provide longer wear than standard MLC flash, but not everyone realizes that eMLC’s superior endurance comes at the cost of slower write speed. By writing to the flash more gently the technology can be made to last considerably longer.
So how do you compare the two? OCZ introduced MLC and eMLC versions of the same SSD this week, and this provides a beautiful opportunity to explore the difference.
As you would expect, the read parameters are all identical. This stands to reason, since Continue reading
Someone recently asked The SSD Guy if there is a way to determine whether an SSD is SLC, MLC, eMLC or TLC.
I found it a little odd to be asked this, since most vendors tell what kind of flash they use in an SSD’s specifications, especially if it’s SLC.
Not finding it there then the next thing I would look at is the price. Raw SLC NAND flash now sells for about 6-10 times as much as its MLC counterpart, so an SSD with a price of around $1/GB is likely to be MLC and one that sells for around $10/GB is probably SLC.
TLC SSDs are really rare. There is the Continue reading
SSD spec sheets, might lead you to believe that power is just not an issue. For example, Samsung lists the power use for a 512GB 830 SSD at 0.127W (typical) for “Active Power Use”. This implies very low demands on the system power supply.
If you do some more research, you find that the peak power usage is a lot higher. AnandTech, in a review article reports sequential write power draw at 5.14W and random write power draw at 5.8W. In that 2.5” SSDs use the 5V power rail exclusively, this is more than Continue reading
I had the opportunity to participate in a round table webinar covering the best practices for solid state storage on July 18. The hour-long session (including Q&A) can be replayed at BrightTalk.
In this round table webinar entitled Best Practices for Solid State Storage Implementation storage analyst Tom Coughlin moderated three of us, Radoslav Danilak of Skyera, Esther Spanjer of SMART Storage Solutions, and The SSD Guy (Yours Truly) in a Continue reading
Today Kaminario added a performance guarantee and a 7-year warranty to its arsenal. The company introduced its “Consistency Under Failure Guarantee” which ensures customers will see no more than a 25% drop in performance during a system failure. This means that critical operations and applications can continue to run at near-standard performance despite the failure of an SSD or even an entire node. Kaminario president Dani Golan told The SSD Guy last week that this is a conservative guarantee, and that few customers see more than a 10% degradation during failure tests in their own production systems.
As for the 7-year flash endurance warranty, no matter which SSD Continue reading
How sensitive are they? Well, I have seen some overblown claims from SSD makers that shock will cause HDD head crashes. I am not sure that I believe such claims, but I certainly do believe that an HDD’s actuator (the read/write head mechanism) can be shaken away from its track, causing a Continue reading
LSI Corp. has launched a new blog that covers (among other things) flash storage. It’s only natural – the company’s SandForce subsidiary is riding high on the SSD wave and LSI’s HBAs are finding widespread use, both internally and externally, in the production of two-hop PCIe SSDs.
TCO has been used as an argument for buying anything from compact fluorescent bulbs to Jaguar automobiles.
The argument usually revolves around an item whose initial price is higher, but which has lower ongoing (or operating) costs, and when these costs are combined, the higher-priced item proves to cost less to own over the long run. In the case of a compact fluorescent (CF) bulb, the bulb may cost $7, versus $1 for an incandescent bulb, but it consumes 18 Watts compared to the 75 Watts consumed by the incandescent bulb it replaces. In addition the CF bulb lasts ten times as long (10,000 hours vs. 1,000 hours.) This works out to a savings of 470 kWh – or about $50 – plus $3 in bulb costs. Continue reading