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Thinking about SSDs …

Posted in General, Storage Applications, Platforms, Storage Interconnects & RAID, Storage Management, Application Environments, Advisor - Neil by Neil

Which of course means I don’t have a life, but …

I once wrote an article called “using high-port-count controllers”. About the only thing I was unsure about was where to put the hyphens. It was all about mixing SAS and SATA hard drives on high-port count controllers. The usual semi-sales pitch for our 52445 product etc. The mentality was basically … use SATA drives for slow stuff, SAS drives for fast stuff and because of these different RAID arrays you’ll need lots of ports.

Simple really.

Then along came Solid State Drives (SSD).

My initial reaction was to go back to Word, use Control+H to replace SAS with SSD and republish (which is what a few of my colleagues seem to be doing). But it turns out there’s more to think about that just replacing SAS drives with SSD drives.

I’ve been talking to more and more people lately who are playing with SSDs … especially the Intel type (flavour of the month so to speak). Surprisingly I’m finding these drives not in the big servers running the massive databai, but in much smaller, often workstation, performance machines.

Now my initial reaction to people questioning me about putting 4 SSD drives on one of our controllers was to ask them what they were now doing with their now unused SAS drives (I was looking for a few donations for a fast system for my kids). Surprisingly the now almost standard answer has been … no, I was running on a single (or couple of) SATA drives before this, often on on-board software RAID.

Wow. I thought moving from expensive SAS drives to obscenely expensive SSDs was a big step, but going from a single-disk workstation to 4 SSDs on a RAID card is amazing - chalk and cheese. Therefore I’ve been asking quite a lot of questions of people, mostly based around the word: “Why?”

Speed (speed, speed and more speed)
Reliability
Speed
Low running costs
Speed
Cool running systems
Speed
Quiet systems
Did I mention speed?

Now you could build a fast system before SSD drives came along. 15K SAS drives have been around for a while, and you could put a pretty quick system together if you have the right skillset and enough money. But not that many people did it. The world tried to use SATA drives to everything. SAS remained relegated to the high-speed database servers as these were the only machines it seemed that warranted such prohibitive expense.

However, SSDs seem to get a different reception from the general public to the old SAS drive. “Yes they are expensive, but they’re fast!” Well so are SAS drives, but Joe public didn’t put them in his workstation.

It seems that Joe public views the SSD drive like the iPhone … not really sure I need one but it’s new, funky, cool, green, the neighbor has one so therefore I have to have one. I’d love to hear from people as to what use they are making of SSD drives. Are you using them because you have a database with 14000 users which just cant run fast enough on SAS, or is because you just want to be at the bleeding edge of drive technology in 2009?

Drop me a line and let me know what you’re up to. It will be interesting to see what different ways people are using this technology.

Ciao
Neil

4 Responses to “Thinking about SSDs …”

  1. Ernst Lopes Cardozo Says:

    Hi Neil,
    SAS (and FC) drives are not fast, they are merely faster. Spinning at 15k rpm and with an average seek time of at least 3 ms, they offer less than 200 IOPS, less than 2.5 times what a SATA drive can do. To use the “multi-tasking” feature, you have to let then work on many requests at the same time, which inevitably means that the response time multiplies. What SSDs offer is not only much higher IOPS, but they doe that with a response time that is almost two orders of magnitude smaller, 0,1 ms in stead of 1 to 10 ms. While they are indeed expensive, the IOPS/$ is today already better than for SAS.
    I recently upgraded my notebook drive and put in a 7200 rpm 320 GB drive. I wasn’t even tempted to look for a 10k or 15k model, but I recon it is the last mechanical notebook drive I’ll ever buy. Next time it will be SSD.

  2. Neil Says:

    Ernst,

    I would agree with your comments if the only configuration we ever looked at was a single drive on a single controller being driven by a single user on a well-powered under-utilised system … in other words my laptop.

    When you put SATA and SAS behind a RAID card the story is somewhat different, however …

    My only concern is the SSD’s problems regarding small writes, which Intel seem to have worked around (if not eliminated). The one thing I have not read anywhere regarding SSD is the failure characteristics of the drives.

    A lot of manufacturers have put a lot of effort into wear-levelling to spread the write-load across the SSD, but I’ve yet to see any information on how these drives fail … whether they start to fail when memory blocks are “worn out”, or whether the drive just stops because one component fails … or whether the drive can work around these issues for any length of time.

    On the notebook front … I am of the same opinion. When the mechanical drive dies in this beast I’m typing on right now (or when the money tree flowers), it will be out with the old and in with the SSD.

    Thanks
    Neil

  3. Ernst Lopes Cardozo Says:

    Neil,
    If data loss due to failing SSDs is your worry, take a look at the ZFS hybrid, where read-optimized SSDs multiply the random-read performance of an array of SATA drives. Since the SSDs are operated as a cache, a failing device can not cause data loss. ZFS checksums all data off-block, so even silent corruption would be caught and the correct data would be retrieved form the SATA disks. ZFS is a fine example of a SSD implementation that goes beyond the drop-in replacement strategy. Oh, and sorry, ZFS has no use for RAID controllers ;-)

  4. Neil Says:

    Ernst,

    ZFS looks to be the future … but not everyone is going to use a Solaris open storage system … I think the variations and innovations will start to flow as people put some serious thought into that rather large pool of existing servers and storage that could do with a shot in the arm.

    Looks like storage just became interesting again.

    Thanks
    Neil

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