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Bottleneck on X1 controller?

Y

yqed

n00b
Joined
Oct 18, 2011
Messages
13
Hi guys,

I'm posting in this forum because is more related to data storage. I purchased recently a HighPoint Rocket 620 PCI-Express 2.0 controller to connect an SSD disk to my Supermicro X7SPA-HF-D525-O motherboard. I read about the X1 bottleneck and I could not find any small sized X4 cards that will fit into my tiny NAS box (Array R2), so I decided to go with the Rocket 620. Based on a FreeBSD read test, the disk can hit 400MB/sec which does not makes me believe you deal with bottlenecks if you use ONLY one disk.

I also noticed that WD had shipped their 3TB (WD30EZRSDTL) model with a Rocket 620. If that card would produce a bottleneck, they would definitely not ship it with, right?
Everyone is posting that a X1 controller will bottleneck. What is your take/advice on that? I don't understand where would be the bottleneck if only a disk is used, are you referring of a bottleneck when 2+ disks are attached to a X1 controller? Because if that is the case, you are right, there will be a bottleneck.

Feel free to also read about my NAS build and how the Rocket 620 integrates into my setup.
 
The bottleneck is not an issue with one 3TB HDD. Really, the bottleneck is with high sequential transfers, so it's not a problem for slower mechanical storage. The 3TB HDD maxes out around 150MB/s, which is like SATA I speeds, and definitely not a problem. With a PCIe x1 2.0 card, I think the limit is 500MBs - overhead.

With the SSD on the 1x card, you'll still be doing better than SATA II, but you won't quite hit SATA III speeds. Of course, most of what makes an SSD so fast is the small file/random performance, and even putting the SSD on SATA II isn't going to change that.

I would tell most people to forget about adding in a 1x SATA III card, and just use the drive on SATA II motherboard ports instead.
 
I see, thanks for the explanation. In my case, I have all 6 SATAII ports used by regular disks and I wanted to add a SSD to cache the read data. So I opted for the Rocket 620 which provided the best of both worlds: very small in physical size and better speed than a SATAII port.

> With the SSD on the 1x card, you'll still be doing better than SATA II, but you won't quite hit SATA III speeds.
I would not worry that much about this aspect, since my SSD disk can only write at 100MB/sec and read at 400.

> Really, the bottleneck is with high sequential transfers
That is the part I'm really interested in, thanks for posting that remark. Does that still applies on SSD usage? The only scenario I'm interested is 1 SSD disk connected to a X1 controller, any other disks being connected through on board SATAII connections.
 
I disagree. The card will not bottleneck an HDD, but it will bottleneck an SSD. And I'm not talking about sequential speeds which aren't very important, but IOPS. SSD should always be used on the main motherboard controller, unless you got an high end controller card (expensive).

With two HDDs on the card, you'll probably see decreased speeds if transferring from one to the other.
 
I don't think the IOPS performance of one SATA III SSD is going to be hampered by one PCIe x1 2.0 controller card. The maximum random 4K throughput is going to saturate less than half of the available x1 2.0 bandwidth.

Like I said, most people with SATA III drives and SATA II motherboards should just use the SSD on the SATA II ports. Since the OP already had the card, there's no reason not to use it, and performance will be better -- if only slightly. But only sequential reads will be affected, and I doubt if it would ever be noticed. Plus, the SSD in question is said to top out at 400MB/s, so I don't think it would be an issue anyway. If it were PCIe 1x 1.1, that would suck.

Ironically, some Marvell and AMD SB controllers actually had a little better random performance than Intel, but worse max sequentials. The good news is it's easy to experiment to find out whether his SSDis being stifled by less bandwidth. Just try it with the RocketRaid, then try it with the SATA II port. See which is better.
 
Aesma said:
With two HDDs on the card, you'll probably see decreased speeds if transferring from one to the other.
Click to expand...
Ya, that will never happen as I only plan to use 1 SSD disk with the Rocket 620 card. In my books, I thought a "slow" SATAIII Rocket 620 port would be better than an onboard SATAII port.

ckryan said:
The good news is it's easy to experiment to find out whether his SSD is being stifled by less bandwidth.
Click to expand...
Just to let you know, the SSD (Crucial M4 CT064M4SSD2) is running on a FreeBSD environment (FreeNAS 8.0.3). It is funny, but you guys posted more useful information in 2 posts than any tech support from Rocket I spoke with. Personally, I ran some basic FreeBSD read/write speed tests. For example the WD20EARS disks I have connected to SATAII ports can push about 280MB/sec reads of the max 300 they can produce. The SSD does 400MB/sec reads through the Rocket card, out of the advertised 500MB/sec.
 
Last edited:
That WD20EARS... no mechanical drive is hitting anything close to 200MB/s, let alone 300MB/s. Surely you're getting some burst or cached results. It's probably closer to 150MB/s in reality.

You would legitimately never, ever notice that reduction in M4 performance on the RocketRaid. The max sequential read and write numbers are rarely ever useful, or relevant to performance. If performance were just about sequential reads and sequential writes, no one would use a SSD -- it would just be cheaper to RAID 0 three or four drives together. But it's not -- small random performance, and low access times are really important. Sequential reads and writes are not as important, but are still important.

It's not as though your M4 on a SATA III port would be twice as fast as on a SATA II. In reality, you would only notice a slight increase in real world performance, not 2x.
 
Man it's great to read all the very good info on storage performance. I have the same controller Rocket Raid 620 on my workstation computer. Since I'm going to use it with single SSD drive might as well keep the controller.:)
 
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