SDHC Cards vs Hard Drive vs SSD

by Jerry Jackson

Almost every modern notebook has a built-in memory card reader, but not everyone uses these card readers for digital photography. Now that SDHC memory cards offer larger capacities at low prices, is this a good option as a second storage drive, or even your primary boot disk? We did some testing to find out just how useful a $30-$100 memory card is for laptop owners.

One of the harsh realities of modern life is that we constantly need more storage space. Between software files, digital images, digital audio, and now digital video we just can't get by on a single 40GB hard drive anymore. But what if you don't feel comfortable opening up your laptop and removing the old hard drive? What if you don't like constantly plugging and unplugging external hard drives and flash drives into your laptop USB ports? Another option is to use the built-in SDHC card reader as a second internal storage drive.

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Our editorial staff first stumbled onto the idea of using an SDHC card as a "permanent" second drive during our review of the Asus Eee PC. That subnotebook only includes a 4GB SSD (or rather built-in flash drive) and it just isn't enough room for most storage needs. That's when we realized a SDHC card could serve as a second drive for everything from files and applications to even the operating system.

As we tested these low-cost storage drives on multiple laptops in our offices we discovered some great reasons why you might want to buy an SDHC card for your notebook ... and some reasons why you might want to consider more traditional storage options.

Performance

In this review we tested several storage options both in terms of SDHC cards and traditional storage like Hard Disk Drives (HDDs) and Solid State Drives (SSDs). The two primary SDHC cards we used for our benchmarks were the 8GB Transcend SDHC card and the 16GB A-DATA SDHC card. Both cards are labeled as "class 6" which means they offer the fastest read/write times currently available for SDHC cards.

Below are standard ATTO disk performance benchmarks used to test the maximum read and write speeds for storage drives. We compared the 8GB Transcend SDHC ($31.99) and 16GB A-DATA SDHC ($64.99) against a 128GB Memoright SSD ($3,399) from DVNation. Granted, this is hardly a fair comparison, but it demonstrates the difference between using an SDHC card and a genuine SSD.

8GB Transcend SDHC:

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16GB A-DATA SDHC:

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128GB Memoright SSD:

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The main point here is that both of the class 6 cards offer similar performance but the genuine SSD is so much faster they aren't even in the same league. Of course, what did you expect from a SDHC card when it's only a small fraction of the cost of a true SSD?

Next, we benchmarked the SDHC cards in both a Dell Inspiron notebook and an Asus Eee PC using HDTune. HDTune is the gold standard for drive benchmarking because it measures the consitency of the transfer rate (basically the read rate) and provides tha access time (the delay between when the computer tries to read data and when the data is available).

We also benchmarked a traditional 2.5" SATA 60GB hard drive (5,400 rpm) and a 32GB Memoright SSD ($999) from DVNation for comparison purposes.

8GB Transcend SDHC in Dell:

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16GB A-DATA SDHC in Dell:

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16GB A-DATA SDHC in Asus Eee PC:

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60GB SATA (5,400 rpm) hard drive:

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32GB Memoright SSD:

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The most interesting item of note in these benchmarks is that the SDHC cards managed to deliver access times similar to that of a genuine SSD. This means the instant your computer needs to find data it is there.

The Limitations

One of the first clear limitations we encountered during our testing on multiple notebooks is that some laptops use slow built-in card readers. If your laptop isn't equipped with a high-speed built-in card reader then any SDHC card you use will run too slowly to be of any practical use as a second drive.

Below is an HDTune screenshot showing just how slow a typical SDHC card is when used inside the built-in card reader on a Fujitsu LifeBook E8410. Keep in mind the card being used in this test is a class 6 SDHC card ... one of the fastest cards available:

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As you can see from the image above, the speed of the built-in card reader can be a serious bottleneck in the performance of the card.

Another common criticism of flash-based storage like SDHC cards is the lack of "wear leveling." Wear leveling is a technique used in SSDs for prolonging the lifespan of flash memory. Flash memory is limited by the number of times data can be written and erased to the medium. Wear-leveling works around this limitation by arranging data so that erasures and re-writes are distributed evenly across the medium. In this way, no single sector of the flash prematurely fails due to a high number of write cycles.

That sounds like an absolutely manditory thing to have in flash storage ... and luckily "high-performance" SDHC cards such as the 16GB A-DATA SDHC card and many other class 6 cards from other manufacturers incorportate wear-leveling.

For example, the 16GB A-DATA SDHC card has an estimated endurance or lifetime of 1,000,000 write cycles. What does that mean is "real world" terms? You would have to constantly write, erase and re-write data non-stop for several years before you need to be concerned about failure.

If your SDHC is 4GB with a formatted capacity of 3900MB, and you do nothing but write to it as fast as you can - at, say, 30MB/s - you'll still only be able to replace its entire contents every 130 seconds. At that rate, it'll take you 1,500 days (4.1 years) to hit 1,000,000 cycles.

In short, by the time you need to worry about SDHC failure we'll probably have 320GB SDHC cards or the computer industry will start using another type of storage medium. That said, every electronic device ever created can fail. We've had brand new hard drives and brand new SSDs fail in our office after less than a week of use. Bottom line, in most cases we don't believe using an SDHC card is any less safe than any other storage methods.

Conclusion

In the end, SDHC cards are a good option for people looking for cheap storage, but they aren't the best solution as primary drives. On one hand SDHC cards have extremely fast access times that even rival expensive SSD storage drives. On the other hand, data transfer (read/write) times are quite slow ... even by slow hard drive standards.

The bottom line is that using a fast class 6 card like the 16GB A-DATA SDHC card in your laptops's built-in card reader can make an excellent second storage drive, but it isn't a great idea as a primary storage drive unless you don't have any other options.

Pros:

• SDHC cards offer cheap storage without the need to open up your laptop
• Removable storage so you can take important applications with you
• Fast SDHC cards have rapid data access times
• Data transfer rates remain mostly constant

Cons:

• Your notebook's built-in card reader might be too slow
• Slower SDHC cards aren't really fast enough
• Even a fast SDHC has slower transfer rates than most hard drives
• Real SSDs are MUCH faster ... and MUCH more expensive

 

Interesting article Jerry. Thank you.

I'd consider using an SDHC card in the same manner I do a flash drive. But as a memory expansion or a harddrive, I would not feel comfortable. Memory Cards including the Secure Digital High Capacity variety aren't stable enough.

 

How did you arrive at these numbers?

(Assume no write-leveling)
If you assume a block is write cycled once per second, then that is 1 cycle/second * 60 secs/min * 60 min/hour * 24 hours/day = 86,400 write cycled per day (meaning the block of storage would be used up in a day at this rate)

If you want the block to last 1.27 years, and assume 100,000 cycles. That means you want the bblock to last 1.27 years * 365 days/year * 24 hours/day = 11125.2 hours.

100,000 cycles / 11125.2 hour ~= 9 cycles per hour = 1 cycle per 6.7 minutes

So, without write leveling, blocks would potentially fail quite quickly. However, you wouldn't lose much storage if one block fails.
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On the other hand, if you assume write leveling is perfectly implemented, then (for a 16gb SDHC) you have 2^32 * 100,000 total cycles. A write rate of 16MB/s corresponds to 2^24 cycles/second. This means the drive would last (2^32 * 100000) / (2^24 * 60 * 60 * 24 * 365) = 0.8 years. At this point, the entire drive fails because all the write cycles for all the blocks are used up.

0.8 years of continuous writing is pretty good, but this is a very optimistic calculation (relies on many simplifying assumptions).

 

Depends on how you use your computer and how you store your files. I personally maintain one desktop with dual hard drives (400GB + 250GB), two laptops with one traditional hard drive each (60GB and 80GB), an Eee PC with 20GB of flash storage (4GB internal and 16GB SDHC), and I have a stack of four external USB hard drives totaling just above a TB in data storage.

In other words, any file or application that's important to me is backed up "at least" once.

Although I would never feel comfortable using an SHDC card in the built-in reader as my primary boot disk for my operating system, I'm perfectly fine running applications off of it or storing documents, videos, photos, or audio.

I trust an SDHC card about as much as I trust any storage device ... I believe it will work, but I will ALWAYS backup my data.

 

This is real delirium.
There is also arithmetic and dimensional mistakes.
Why difference between 100,000 and 1,000,000 after formulas is only 5.1/1.27=4? Why not 10?
Result of this "formulas" gives [MB*year/day^2], not [year].

 

Bad math ... that's what I get for trusting another website's arithmetic. I'll recalculate and publish the new figures.

Okay, I've published some fresh math. I believe this makes a great deal more sense. Feel free to challenge my arithmetic ... it's Sunday morning and I just woke up.

 

I can't believe that card reader on the Fujitsu is so slow, only 3mb a second transfer? Thats a real shame.

 

I understand the calculated mtbf for flash drives but.....is it just me or has anyone else seen these fail at a greater frequency. I have been through a few in the past two years, each arriving at a point that the system just doesnt recognize them anymore.

I cant imagine getting a year out of one when used on a daily basis just to transfer a few files between work and home.

 

Is an SDHC stable/fast enough to be the primary boot disk? By fast, I mean faster than 7200RPM HDD's, 'cause it's pointless otherwise.

 

The math is correct this time; however, it fails to address the hypothesis that write-leveling is not needed. In fact, your calculation assumes write-leveling is implemented (this is basically what you are saying in this assumption: "you'll still only be able to replace its entire contents every 130 seconds.")

The real point is that if write-leveling is not implemented, then some blocks would be written to more often then others, causing them to fail more quickly.

 

I just got off the phone with technical support from Transcend and checked the websites for A-DATA and another SDHC card manufacturer called Apacer. All three companies confirmed that their Class 6 SDHC cards DO in fact use wear leveling.

According to the customer support teams for all three of the flash manufacturers listed above, all of their Class 6 cards have the following specifications:

• Support CPRM (Content Protection for Recordable Media)
• Support the interface of the SD 2.0 Standard
• Support Error Correcting Code (ECC) function to detect and correct errors
• Support in System Programming (ISP) function to load the firmware
• Support Wear Leverage function to maximize data endurance

I've updated the article to reflect this new information. Apparently, most old SD cards and non-Class 6 SDHC cards do not support wear leveling ... which is why I originally wrote that these cards do not include wear leveling.

In short, most (if not all) Class 6 cards from reliable manufacturers should use wear leveling.

Bottom line, wear leveling shouldn't concern you unless you're using cheap SD/SDHC cards.

(Man, I should ask for a bonus for all this weekend work.)

 

In my opinion, no, SDHC cards aren't fast enough to be used as the primary boot disk unless you have no other choice ... or unless you're talking about using a VERY old hard drive (slower than 4200rpm).

My personal experience with using SDHC cards in a HP dv6000z and Asus Eee PC at home is that these cards are reliable enough and fast enough to use for various applications but not if speed is your primary concern. I have a couple programs that I have on an SDHC card that I run on multiple computers without having to install them on each computer's hard drive. Plus, in the case of the tiny Eee PC, SDHC cards can make a good solution if you can't fit another hard drive inside your computer.

 

I see... Well for me, lately I've been wondering if there's a cheap way to increase boot times to faster than what a 7200RPM can do. But after reading the CF to IDE article and this one, I guess there's only a genuine SSD that tops 7200RPM...

 

On that note, keep an eye open for the top article on our home page tomorrow morning.

 

Hahutzy...

If you want to increase your boot times, see the Tips and Tweaks thread hyperlinked below.

 

Flamenko: I'm using XP, will those tips and tweaks apply?

 

great article overall. I am considering a purchase of the EEE pc. I have looked at the Cloudbook too, but the early review of the Cloudbook lead me to believe that the chips seem to be stacked in the favor of ASUS. The hard drive size on the Cloudbook is nice though.

 

Apologies....although Im sure some will, I havent tested on XP at all.

 

Jerry, great article. But something is drive me crazy. In the first photo of the ASUS there are two things plugged into the USB ports... one is obviously the transmitter for the LogiTech Nano mouse... but what the heck is the other thing?

 

One is indeed the Wireless USB receiver for the Logitech Nano mouse. The other is a mini Bluetooth 2.0 +EDR adapter.

http://www.cirago.com/docs/html/Cirago_BTA3210.html

It's the perfect way to add Bluetooth to the Eee PC. Several other companies are releasing tiny Bluetooth adapters this year, including Belkin and Princeton, so you should be able to find these adapters all over the place pretty soon.

As soon as I find a Bluetooth mouse that I love as much (or more) than the Logitech Nano I will stop using the Nano and just use a Bluetooth mouse ... thus freeing up the other USB port.

 

are all integrated SD media readers in notebooks compatible with SDHC cards, and how do we know if we have a slower reader?

I've gotta HP nc8430 if that helps.

 

You'll need to contact customer support for your laptop manufacturer, or look up the info on their website. You can also see if the SDHC card manufacturer knows.

Most laptops with SD card readers built since late 2006 have SDHC-compatible card readers ... but not all of those readers are capable of reading from or writing to the SDHC card at a reasonable speed.

Again, three of the laptops I tested ran Class 6 SDHC cards at about the same speed ... but the built-in reader in the Fujitsu notebook I tested ran the SDHC card at only about 1/6th speed (3MB/sec rather than 18MB/sec).

 

Interesting. However, wouldn't it be easier to plug in an external drive, and have much more storage that is seemingly more reliable?

 

Yes, but then there's the issue of hauling around an external drive. Some (not most) people would rather have a compact "internal" solution rather than bring yet another device with them everywhere they go.

 

Hey Jerry, off topic but is that a Cirago micro bluetooth adapter I see? (next to the VX Nano adapter)

hope SDHC cards get larger and cheaper, great for external storage.

 

Yes, it's the Cirago Bluetooth 2.0 +EDR adapter ... see my response on page 2 of this thread.

32GB Class 6 cards are coming soon/later this year and rumors are 64GB cards are just around the corner ... so prices on the 32GB and smaller cards will drop even more as these higher capacity cards become available.

 

I thought SDHC only goes up to 32Gb... Can we really expect "SDUHC"s to come out soon...?

 

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How has that Cirago BT dongle worked out? We were experiementing with one for a clients product but decided not to for reliability reasons. After about the third removal it broke. The plastic lip which held the PCB in place snapped off at both sides. A patch and a few more install / removals later the rear bezel pulled the same stunt... Nonetheless we declined its use for the product. Too bad since the size was fantastic!

On another note, I use SDHC cards as an intermediate synch backup for some folders on my HDD. Using Comodo's synch tool I can automatically have a back up running on a few key files. They are also a handy place to store .pst files or other data which you may need to switch quickly between laptops (as I often do). The biggest problem doing this is the card stability during a standby or shutdown. If a synch is currently active it can cause the card to stall which reeks havoc on the restart. But by managing the synch settings and using a good card I find this to be an extra little insurance between the home an office and all places in between.

 

I likewise had a breakage about 3 weeks after I bought my Cirago BT adapter. However, a small drop of super glue was all it took to make the adapter rock solid. I haven't had a breakage since and the adapter itself works flawlessly.

Yeah, I wish it was built well enough that I didn't have to use super glue to fix it, but it's fixed now ... and if it ever breaks again it was cheap enough that I can replace it with another one or maybe a better built BT adapter from another company.

 

I would consider getting a 32GB one just for the Vista bootup but I am weary of how the max and min speeds are(15~mB/s) . I wonder, has anyone actually put Windows on one of these things?

 

I've been trying, mostly just out of curiousity, but I've been utterly unable to boot off my sd card reader

 

just say I dont think the laptop user reluctant to use external devices.

But the brand maker willing protect there product, since several year the SATA drive was a standard of PC, but now no one of brand maker laptop, has propose a connector external of SATA drive to have a fast and usable external connectivity.

also no one brand maker of laptop has a laptop PC have'nt any rotative internal devices, (without CD/DVD HardDIsk drive).