Which drive to use?

August 11, 2011

Question to the Storage Advisors: We are setting up a small RAID6 on a dedicated server with 5 drives initially (it may be expanded later). The array will store mostly video content and will serve a maximum of 2-3 clients at the same time, reading those videos for playback/editing. The question is what disks to use – we have to choose between lower power 1.5tb drives with decent read/write performance but modest IOPS and higher speed drives with comparable read/write performance but nearly double the IOPS. The question is really one of cost (the high speed drives are over 60% more expensive) – will the higher I/O performance make a big difference to these types of file serving workloads under RAID 6? Or is the money going to be wasted? Thanks for any response you can offer – Dimitri.

Dimitri … good question and one that will have a major impact on the overall cost of your server. Since you haven’t mentioned drive models I’ll be generic, but your mention of 1.5TB drives is a giveaway for Seagate desktop (AS) drives … one of the cheapest drives on the market today.

Firstly, SAS is a waste of money and time for your intended scenario. SAS drives have very high rotational speeds, and very low seek times (and hence high IOPS), making them great for database servers and transactional workloads where small amounts of data are required on a regular basis. However their MB/sec throughput is not that much greater than SATA drives (roughly speaking) so you won’t get much of a performance improvement for your dollar by using these drives in a video environment.

SATA drives come in two flavours from almost all drive vendors … desktop and enterprise versions. Technical speaking the drive vendors will tell you there is a great deal of difference between desktop and enterprise drives, and as far as we are concerned there are some major advantages to enterprise drives (TLER for one) which make them suitable for RAID environments. For this, and purported reliability issues, I’m going to say go for enterprise level RAID SATA drives for your server.


In your question you were concerned as to whether the higher IOPS of (I presume) SAS drives will help your server. Basically … No. IOPS is how we measure small random data loads (Input/Output Operations Per Second). That is not the data type you are described for your server. A video server does “streaming” data … large amounts of data written or read from the drives in a single stream. SATA drives are just as quick as SAS drives in this environment. While SATA drives can’t match SAS drives in the IOPS department (slower seek, rotation etc) once they start delivering data they can keep chugging along with the best of them.

Therefore, for video applications, use SATA drives. Their MB/sec combined with the cache on a RAID card will allow for very high sustained speeds at a fraction of the cost of SAS drives. They are also much larger, so you need a lot less of them to get up to the capacities required for video storage.

So the choice is simple … SATA over SAS for video. That just brings us back to the question of “desktop” drives vs “enterprise” drives (as defined by the hard drive vendors). If your question is really whether to opt for either of these types of drives I’m going to opt for the enterprise drives in a RAID environment no matter what the cost of the drive over the desktop drive. While there are a million studies out there and much anecdotal evidence that one is or is not “better” or “more reliable” that the other … it is our general experience that as desktop-level drives get bigger compatibility and reliability becomes more of an issue, so while there really won’t be any speed difference between the desktop and enterprise drives in your scenario, there will be (I believe) far fewer problems using enterprise SATA in a RAID 6 video server.

With only 5 drives in the server the overall cost difference is a small portion of the overall price of the server, and I believe you will be better served by using drives that drive vendors intended to work with RAID, not the cheapest of the cheap desktop units.

Now, while we are on this tack … you’ll notice I mentioned cache on the card a little further up this blog. Yes it’s there and yes, you need to protect it. While you can put a battery on one of our 5 series controllers, why not look at the 5Z range of controllers … no batteries, no hassles (zero maintenance as my American bosses call it), no wuckers as an Australian would say. The 5805Z teamed with enterprise SAS drives will give you a reliable fast server that will protect your data for years to come (there, I’ve done the sales bit the boss is always asking for).

Spend wisely, but don’t skimp on the bits that really count.



2 thoughts on “Which drive to use?

  1. Santosh,
    The customer has 2-3 users reading video. My assumption is the would read the video, edit till the cows come home then re-write. I don’t see the need for anything more than decent SATA drives. Of course prices and the model ranges have changed a lot since I originally wrote this, but SATA is still good enough for this customer.

  2. What about “capacity” nearline (“near online”) SAS drives such as the Seagate Constellation ES through ES.3 series of SAS 2.0 drives?

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