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SAS vs SATA: SATA on the ropes.

Not sure if I mentioned this before, but I’m a geek. I like blinking lights and shiny things. I do math and physics for fun. I’d chose a good computer magazine over Maxim. . .well, maybe not THAT much of a geek, but you get the point.

So what’s provoked my geekitude this time? SAS benchmarks!

My friend Karl and I go back and forth about SAS disk benchmarks. I follow him in his quest to get past the 200MBps ceiling on his desktop. I poke fun at his pursuit while secretly hoping he’ll find that right combo to break the 200MBps mark so I can buy it.

Further fueling my mental yoga over disks is the fact that SAS has invaded our server room at work like a plague. A good plague, but a plague all the same. I went to work one day and realized we don’t use SCSI in anything but our older legacy machines. Honestly, I love it, the performance of SAS drives is great, they are small (we use 2.5-inch SAS on IBM blades) and they don’t make as much noise or heat, don’t use as much electricity and have a reasonable capacity.

So what’s the problem? The problem is that I go home (well, sometimes, anyway) and I don’t have SAS at home, I have SATA.

Mind you, my SATA array sits behind an Areca 8-port RAID controller with 128 MB of cache on a PCI-Express based card, so it’s no slouch. But it’s not SAS, not by a long shot.

I now.  . .must. . .have it. I neeeeeeeeeeed it. I don’t care what body part it’ll cost me! I want the speed and lightning response I get when I click the start menu or do some data migration chore on a SAS-based machine.

Vendors are now offering SAS cards with no RAID 5 or write cache available for about $150. The drives are about $250, which makes a small array at home not out of the question. (I just have to come up with a compelling argument to submit to the home finance committee. BTW, consider this an official cry for help to come up with an argument that will avoid the dreaded giant red “Denied–resubmit in 90 days” stamp the chair of said home finance committee has in her possession.)

But while trying to come up with this argument, it hit me. Traditional SCSI is dead as a doornail, and I missed the funeral.

In the meantime, if SATA ever slows down in its capacity growth, it had better look out too.

If I’m willing to sacrifice a bit of space for the speed, who else out there is willing to do the same? A decent capacity SATA disk will run you $200;  a 150 GB Western Digital Raptor (10k rpm SATA) will run you $220. So why bother? Why not spend the extra $30 and get SAS? The controllers are about the same cost now for quality brands, the cabling and power envelope are roughly the same, acoustics on the 2.5-inch drives are not bad and the thermal footprint is not outrageous.

And there’s a downside to size. How long would it take to rebuild a RAID 5 or 6 array made up of 4 TB drives ? How would I cope if I lost 4 TB of data?

My future holds a 32 GB to 64 GB RAID 1 solid-state disk for my OS, with capacity SAS for the 3 TB that Office 2010 is going to take up. IBM has already released a 16 GB SSD for their blades with the 32 GB models soon to be widely available. Not only that, but you can set them up in RAID 1. (Every time I say “RAID 1 SSD” I have to giggle.)

Can someone give me an irrefrangible (Thanks for the SAT submission! More more!!!) argument why SAS will not someday soon be the SATA of today?

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LOL - I have the same argument. I saw the greatest enclosure at MicroCenter last week, 4x 2.5" SAS/SCSI drives (since it's just pass-through at this point, it doesn't really matter which you use, the pinout is the same) that fits into a 5.25" half-height enclosure, basically the size of a CD-Rom drive. Now I looked at that, for a price tag of about $70, and thought what every storage geek thinks: I have 3 bays in my server, that's 12 drives, right? As I've said before, I can't, (and couldn't) see the demand for speed in any home-based application, so I went with SATA-II on my multiple terabytes of storage. I don't know, maybe I'm not geek enough for this blog. :) Jesse G.
Oh - and on the note of the finance committee. God only knows, I've learned though that it's easier to ask forgiveness than permission. :)
I use Windows Vista for some of the stuff I do at home, I have a SATA-II disk and when I play Simcity 4 and alt+tab out then alt+tab back in my disk spends 4 minutes doing stuff... What exactly, I don't know, but 4 minutes of my life is sucked away by it. My computer is newer (dual core Intel), the disk is SATA-II 300 w/ NCQ. Funny thing I don't have as long a wait for disk access on my XP or Linux based physical machines. I also run Vmware on my home array to virtualize my content filter (I have an 8 year old that likes Pokemon, so I filter EVERYTHING that comes in the house) along with other services I offer to the users I also call my family. Vmware is acceptable and I considered it even fast until I used these SAS drives at work :). One of the services I offer the family is streaming video, I digitize the kid's DVD's so I don't go broke replacing them after the youngest uses it as a chew toy. I serve it up to a couple computers different computers. All this and more off one array and controller. Oh you are geek enough hahaha you do the same math almost all geeks do: 4 bays x 3 drives per bay = Sweeeeet!! I like that advice, I think I'm gonna stop by Best Buy on the way home today :) wish me luck!!!
Hello, good blog, and i am just thinking the same thing. Also realizing how "big" of a stoage geek i am. I use to run SCSI 160 10k's and loved it, I still think it is faster then my single SATA, and about as fast as my striped SATA array. My hang up is cost, 4TB SATA RAID5 = cheap, 1TB SAS RAID5 = Dead and buried. Even with two 36G 10k/15k striped you are looking at quite a cost, though i could get away with that expence. If you did get it how is it working? Have you benchmarked it to see what you are getting? What kind of load times? Trasfer rates? How much to you love it? :-)
Thanks, :). I've been tracking SAS disks on and they aren't bad, but you are right there is a cost advantage for SATA. I haven't built or bought a SAS array quite yet, my buddy Karl has the Adaptec SAS controller w/ 128mb onboard RAM, he hasn't settled on what drives he wants yet, the controller won't do write cache w/o the battery (100$+ option) so his numbers are w/o write cache. He tried it w/ some first generation SAS drives from eBay and didn't hit his magic 200MBs sustained so he's back to hunting for drives. I'm waiting in the wings :0 living vicariously. Hahahaha.
Arguments I can't give you-- unless your financial approver appreciates a blazing fast disk subsystem! My main Windows box is based on an Intel D975XBX2 + Dell PERC5/i RAID0/1/5/10 controller with 256MB cache. The fact this combination *works* is a critical thing. The PERC5/i is a fairly inexpensive board, but the price paid is that it's pretty much only compatible with systems based on the 975 or S5x00 chipsets (the same as those found in Dell's workstations). Connected disks are two 73GB 15k 3.5" drives, silent as hell, and three 250GB SATA-1; all RAID-0. It is verydamnfast. @ 15k the SAS disks deliver access times in the low 3ms range, and I expect 2.5" 15k units would improve upon that. Real-world transfer rates are mostly bottlenecked by everything else on my LAN, but I've seen steady 147MB/sec writes. Just do it. It's not that bloody expensive anymore, and it's completely worth it!
Jeremy, you had the same response I did!! I don't know if hellafast is a word but it should be used to describe setups like you've mentioned. How do the SATA RAID 0 compare to the SAS? Take a peek over at my follow up blog post of a setup similar to yours.
"Oh - and on the note of the finance committee. God only knows, I’ve learned though that it’s easier to ask forgiveness than permission. " Thats a slippery slope and generally a two way policy. On SAS being better than SATA - other than bragging rights i remain unconvinced that its more than marketting features at this point.