back to article Let's talk about the (real) price of flash and spinning disks

Lately I have been writing a lot about the role of flash memory and disk drives in the future of storage infrastructure (here and here are a couple of examples). And it's clear flash will be used for primary workloads, and object storage and disks for the rest. The reality is that flash memory is quickly becoming already a no- …

  1. Anonymous Coward
    Anonymous Coward

    What about 3D?

    The imminent availability of 3D Flash will create a huge discontinuity in the relative cost per GB of Flash vs. HDDs.

    1. Gordan

      Re: What about 3D?

      The price per GB of SSD is already down to around 5:1 mark if you consider like for like (1TB 2.5" 7200rpm disk vs. 1TB 2.5" SSD).

      Flash also tends to be much more reliable than spinning rust. Sure, there's the write endurance limit on flash, but this is a complete non-issue in just about every sane use-case:

      http://techreport.com/review/27909/the-ssd-endurance-experiment-theyre-all-dead

      Consider that most of the tested SSDs survived 1PB (yes, that's _peta_) of writes, with some surviving as much as 2PB. To write that much data to them took between 1 and 2 years of continuous writes. To write that much data to a mechanical disk in random order, would take many, many times longer. Sufficiently longer that you would be similarly looking at about 100% failure rate over a similar write volume. Then consider that write:read ratio is typically less than 5%, and that a mechanical disk suffers wear regardless of whether an operation is a read or a write (bearings and actuators will only survive so many seeks and revolutions) you are looking at a real life expectancy of an SSD that only suffers wear on writes that will on average vastly outlive a mechanical drive.

      Spinning rust is increasingly struggling to maintain it's relevance in most environments.

  2. Lusty

    IOPS

    The article is talking about random write IOPS presumably (not even remotely explained). While sequential read IOPS makes far less difference, so for requirements such as large media files (4k video for instance) SATA drives would still win for performance/cost over ssd because for streaming the interface is often the limiting factor, flash only really helps when the workload is random once you hit a certain (quite low) number of drives. The maths is easy on this one, just work your way back from the bandwidth on FC, SAS or iSCSI and divide by IO size or throughput to work out where the line is drawn between the technologies.

    1. defiler

      Re: IOPS

      For single-user streaming, spinning discs are an easy sell, but if you scale out to a hundred users streaming different streams at the same time then you're not far off random data again.

      I know, you can have the OS pre load lots of data while the head's looking at one stream so it's not a total disaster, but then you're moving the problem to RAM. And that costs more than flash. Just a thought...

      1. Paul Crawford Silver badge

        Re: IOPS

        There is no "one size fits all" unless price is no object. For your use-case you have to decide how much IOPS you need, how much data you need to store, and how much money you are prepared to spend.

        I suspect the majority of users would currently be best served by a combination of HDD and flash. Some file systems like ZFS have built-in support for using separate storage for write intent logs, so using flash for that is a very cost-effective gain on the write side. For reading you can also have read-optimised SSD for the cache to help with frequently accessed data. Other systems also support data tiering so you can balance cost and performance in an intelligent way. The Devil is often in the detail.

        1. Lusty

          Re: IOPS

          I wasn't saying flash is bad, just that IOPS are pointless in certain scenarios because various other things limit performance. Most people don't even realise that a SATA SSD limits IOPS because the SATA bus speed is insufficient and that a PCIe flash device is better as a result (by a massive wide margin). Amazingly Apple are one of the few to notice, hence they don't have any devices with SATA Flash..

    2. Nick Dyer

      Re: IOPS

      Great point, this is usually the unspoken 'Achilles Heel' of All Flash propositions; sticking a sequential workload on it really won't make it go that fast!

  3. Frenchie Lad

    Insight

    I'd prefer to see some sort of insight being offered in the article rather than just stating the obvious.

  4. calmeilles

    Power?

    Real life measures for power and cooling late last year SAS cost about 100p per gig per year, SATA 50p per gig per year, Flash 12p per gig per year for a head and 7p per gig per year for a dumb-ish shelf.

    There's a lot more to the TCO or cost efficiency than either capital outlay or iops.

    1. Paul Crawford Silver badge

      Re: Power?

      "SATA 50p per gig per year"

      So my home RAID with 12TB protected space from 5*3TB HDD is going to cost me £6000 per year in power! Are you quite sure?

      1. John Brown (no body) Silver badge
        Joke

        Re: Power?

        Maybe he's talking about a very large data centre with highly inefficient cooling systems. In Death Valley. In the Summer.

      2. Lusty

        Re: Power?

        To be fair, you probably don't have diesel generators, industrial UPS, air conditioning and monitoring systems in place within your "power and cooling solution" at home. Which was his point. Looking at the numbers without understanding the whole picture just leads you to a bad conclusion. I've no idea if the numbers were correct but certainly industrial UPS is expensive as hell because you need to swap the batteries out regularly, and you have to have N+1 of everything. Same with the generators etc.

        In pure power costs though, I do know a server from a few years back would consume enough energy that power cost more than the device over 5 years.

        1. Naselus

          Re: Power?

          I'd still have the backup generators, UPS, air con and monitoring on my server room regardless of if it's Flash or rust-on-SATA, though. Plus, I'm not exactly buying a new air con unit every time I add a hard drive to the DC. So it still requires at least 38p of the difference to be purely on the drive's efficiency - which is just as ridiculous a claim, as anyone with a 1TB drive in their laptop will tell you it doesn't cost £380 a year to run the thing, even going 24/7.

          1. Lusty

            Re: Power?

            Again though you're concentrating on price not cost. The capacity of a ups, generator and cooling must be related to load, and spinning disks have significantly higher load which is more constantly high than their flashy brethren. Flash drive power usage is related to the data going in and out while spinners use power all the time if you need responsiveness.

            The true cost of the infrastructure must include the various maintenance contracts in place which are also based on capacity loading. Bigger cooling means bigger bills which are far from small bills.

            Regardless, my point was that the cost of power for a disk in the data centre is nothing like that of the same disk in your under stairs cupboard. The two are not comparable in any way.

  5. Anonymous Coward
    Anonymous Coward

    SAS Disk

    "It’s also quite clear to me that the big loser here is the 10K SAS disk. It doesn’t come out the winner in any comparison"

    How about data written and life time. I know of legacy servers with disks spining for a decade*, how long is the new "enterprise" MLC going to last?

    * I would want to cold boot them

    1. Lusty

      Re: SAS Disk

      "I know of legacy servers with disks spining for a decade*"

      Running servers without support is your own call, as is running legacy hardware which begins to become a risk nightmare the older it gets thanks to lack of available patches and spares.

      In the real world, as long as I'm not swapping MLC units out every two weeks I couldn't give a monkeys how many failures I get because the vendor will swap it out and I won't lose data because I have more than one disk.

  6. bbulkow

    Prices for flash are wrong

    By lining up consumer rotational drives against enterprise "SAS" flash, this artical does the reader no favors.

    At time of printing, the first 3D Flash has just come available, with 1T SATA drives costing between $600 and $350, where the rather excellent Samsung 850's are on the higher end. I have seen drives like this - SS 840's, 843's, and Intel 320's bought years ago and still running. Lower power means lower strain.

    In 3 years, we will have hybrid systems - but the two layers will be RAM and Flash. The next drop in Flash prices will shock anyone with a major investment in "hybrid".

    1. Paul Crawford Silver badge

      Re: Prices for flash are wrong

      "To be fair, a consumer-grade flash drive (with SATA interface) is only 10x the $/GB of a SATA hard disk"

      It was mentioned, and for fairness it also has costing for both "consumer" and "enterprise" SATA disks (really, use the SAS version for high-capacity HDD for various reasons to do with reliable identification and proper command queuing, but the pricing is not so different these days).

  7. Gordan

    +1

    I just bought some 1TB SSDs for £225 each. That is a large multiple out from the price quoted for flash.

  8. MityDK

    Apples and Oranges, mate

    This article was supposed to be about the REAL costs of spinning vs flash. Real costs take into account things like maintenance, power, cooling, rackspace, support, and also look at data efficiencies which flash is built around, deduplication, pattern removal, compression etc which are the hallmarks of all flash or hybrid type solutions.

    I find this article to be unserious. I feel like the author is trying to prop up the horse and buggy market by telling us combustion powered cars are more expensive and will continue to be for some time.

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