eSATA and expresscard

[rawdawg]

Let me reask this...

The MBP has one expresscard slot. So if you use an eSata adapter (even if it has dual eSATA ports) it would only have one eSATA channel..... And that would be limited further by the express card slot and more still by the type of card (make, model, etc..).

My question is: with Barefeats claiming even the best eSATA card for a MBP being 200MB/s (even if you claim less) using a dual eSATA RAID connection for a stripped array would be limited to 100MB/s per port.

Is this correct? Because I'm trying to understand this to see if it's worth building a RAID setup for my MBP when I'm home.

I've asked this numorous times and get helpful advice but not addressng this specific and fundamental fact. I am not interested in FW800 because I want the fastest I can get but want it to make sense. I would also reask my other questions about my situation but this question comes first.

 

[jrlcopy]

What you'd want to do is buy an external raid that has an esata port. You wouldn't want your esata or osx to manage the raid itself.

This way you can have those 10drives or whatever in the box linking over 1 esata cable to your mbp.

How I hate that the new mbp's don't have an express or esata port. I was in that 'single digit percentile' that used it every day.

 

[rawdawg]

What you'd want to do is buy an external raid that has an esata port. You wouldn't want your esata or osx to manage the raid itself.

This way you can have those 10drives or whatever in the box linking over 1 esata cable to your mbp.

How I hate that the new mbp's don't have an express or esata port. I was in that 'single digit percentile' that used it every day.

thanks. I bought the 17" specifically because it retained the expresscard slot.

But my question isn't about the external setup. It's about the eSATA interface capabilities of the MBP. For some reason whenever I try to ask this it gets sidestepped and it in fact is the critical question.

I've heard there is no performance gains from single eSATA RAID enclosures. This is because in order to get any performance advantage from stripping you need more than one data channel to deliver the data. So even with your example you wouldn't going performance unless the enclosure had at least 2 data channels.

Now the main question is because there is only one express card slot on a MBP wouldn't that mean there is only a single data channel??? That even if you have a dual eSATA card it still has to split info through that SINGLE data channel.. Therefore couldn't someone surmise there is no benefit gained with a MBP by stripping (or RAID0)!!???!?!

I've asked this multiple ways in multiple posts but people keep dodging the question. It's like asking what your favorite food is and people keep saying, "yeah, Seattle can get rainy sometimes"... sorry, I do appreciate people taking time to respond. It would just be more helpful if it stuck to my questions.

thanks

 

[m85476585]

You can get up to 200MB/sec, or maybe a little less depending on how much overhead there is. That is the limit of the expresscard slot. It doesn't matter how many cables you use, or how many disks you have. Since 200MB/sec is less than the limit for 1 SATA cable, you won't gain anything by using 2. They make eSATA cards with 2 ports, but the 2 ports will share the same 200MB/sec. Some cheaper cards might not give you 200mb/sec at all, and certain cards tend to cause kernel panics (see the really long "E-sata Express card , which one actually works" thread).

You will have to read more about specific enclosures to see if you will get any increase in speed from them. You will theoretically get some speed increase because most disks will not read at 200mb/sec. For example, my fastest disk peaks around 130mb/sec, and if I put 2 of them in a RAID enclosure connected by eSATA, I should get 200mb/sec assuming the enclosure and my eSATA card work as advertised.

 

[rawdawg]

You can get up to 200MB/sec, or maybe a little less depending on how much overhead there is. That is the limit of the expresscard slot. It doesn't matter how many cables you use, or how many disks you have. Since 200MB/sec is less than the limit for 1 SATA cable, you won't gain anything by using 2. They make eSATA cards with 2 ports, but the 2 ports will share the same 200MB/sec. Some cheaper cards might not give you 200mb/sec at all, and certain cards tend to cause kernel panics (see the really long "E-sata Express card , which one actually works" thread).

You will have to read more about specific enclosures to see if you will get any increase in speed from them. You will theoretically get some speed increase because most disks will not read at 200mb/sec. For example, my fastest disk peaks around 130mb/sec, and if I put 2 of them in a RAID enclosure connected by eSATA, I should get 200mb/sec assuming the enclosure and my eSATA card work as advertised.

Most helpful answer so far! Thank you.

So that's how eSATA with RAID 0 can still have benefits... Because the eSATA connection is faster than the drives, and therefore stripping them you can get the most from the eSATA connection. So when you say "Since 200MB/sec is less than the limit for 1 SATA cable, you won't gain anything by using 2." you mean unless you RAID (of course I wouldn't have 2 cables going to the same single drive.... When I suggest multiple cables of course I'm referring to multiple drives).

How about the ability to use 2 FW800 channels with a FW800 expresscard adapter. Wouldn't you then have 2 FW800 channels and therefore more throughput for RAID than a single 200MB/s eSATA connection could offer?

 

[m85476585]

2 FW800 channels will give you about 154MB/sec (since I get 77MB/sec real-world speed on FW800).

There are basically 2ways to do an eSATA RAID setup. The best way is to get an enclosure that holds 2 drives and handles the RAID for you and connects to the computer with a signe eSATA cable. The other way is to get 2 enclosures, 2 drives, and a 2-port eSATA card, then do the RAID on the card or in software. You won't get any more speed with the second option, and it might be slower because of the software RAID.

Here's an example
http://eshop.macsales.com/item/Other World Computing/MEFW936AL2/
It holds 2 drives and connects to the computer with a single cable, either eSATA or FW800. If you use eSATA you should be able to get 200MB/sec, if you use FW800 you will only get 77MB/sec. (There are 2 FW800 ports on it, but that is for daisy-chaining FW800 devices, not connecting the enclosure to 2 FW800 ports on the computer. That won't work without separate enclosures for each drive).
You might be able to find a cheaper enclosure with just eSATA.

 

[m85476585]

If you found a 2-port Firewire 800 expresscard that could give you full speed on both channels at the same time, you could get 77MB/sec*3, or 231MB/sec. I don't know if any FW800 expresscards will give you the full speed on both channels at the same time or if they are limited to the speed of one channel. You would probably have to get one and test it out.

I would just go with a 2 drive eSATA raid enclosure, though. The extra 31mb/s probably isn't worth the complexity and having to use software RAID.

 

[rawdawg]

Matt,
Thank you so much for answering my question about if 2x FW800 is faster than eSATA. This makes sense!

Also, thanks for the recommendation and advice on enclosures. Originally I was looking at these enclosures for dual eSATA this or this.

But as you can see they both differ from your recommendations in that they are a single enclosure that has 2 eSATA ports. Since you cannot daisy chain eSATA (as you explained why your suggestion has dual FW800 ports) I assume that's because these enclosures take advantage of allowing each drive in the dual enclosure to have it's own eSATA cable.

And this type of enclosure is half the cost of the other OWC enclosure you recommended. (Does your have a RAID card though, since it only has a single eSATA cable? Mine would require software RAID or on the card (which I haven't found... have you?)

Which would you recommend?

 

[m85476585]

My 2-port eSATA card doesn't do RAID by itself. I think there is a way to set up software RAID in OS X, but I've never tried it. It looks like you just make a RAID set in disk utility, but I don't know if there are any restrictions such as requiring disks that use the same interface.

Both the enclosures you linked to will require 2 eSATA cables, so you will need a 2-port card. The enclosure I linked to handles the RAID internally, so it only needs one eSATA cable. There should be little or no speed difference between the two, but RAID in the enclosure (and a single cable to connect to the computer) is simpler, and may be faster since the OS doesn't have to do software RAID.

I don't have any specific recommendations for an enclosure. I haven't used one, and I have never tried software RAID in OS X. I really don't have any experience here except knowledge of what all these products should do. In reality, RAID can be tricky to set up, and there is a lot that can go wrong. It's good to hear you plan on backing up to a separate 2TB drive.

A few examples of problems you might run into:
-Not all disks are designed to operate in RAID. Some will stop responding for a few seconds if they encounter an error, making the controller think the disk is broken and with RAID 0 the array might become inaccessible.

-I don't know if the eSATA card has to be compatible with the enclosure. It should just work, but there is always a chance you will run into problems

-Most of the RAID enclosures on Newegg get a lot of bad reviews. I don't think I would recommend any of them except the ones made by Icy Dock, but those are overpriced.

To summarize, a one-cable RAID enclosure will be simpler, but maybe less likely to work and more expensive. A 2-port setup will require a 2-port eSATA card and might put more load on the CPU since RAID will be done by software. You might get more feedback, though, since OS X will know the status of both disks, while with RAID in the enclosure the OS just sees a single larger disk.

Before you spend a bunch of money on an enclosure and drives, make sure you can get an eSATA card that works reliably. I've had numerous problems with mine (both of them) causing intermittent kernel panics, and more recently an instant kernel panic when I plugged it in. You should read this thread
https://forums.macrumors.com/threads/678101/
before buying an eSATA card.

I'd encourage you not to make a decision to purchase something solely based on my advice. Figure out what eSATA card works best with macs, read reviews for RAID enclosures, and see if you can find anyone with a setup that works. Also do some research about RAID and what kind of disks work best (though it might be hard to find info about that). If you do decide to buy something, it's probably a good idea to make sure you can return it if it doesn't work.

If Apple added an eSATA, USB3, LightPeak, or Firewire3000 port to the MBPs, this would be a lot easier. Unfortunately the latter 3 are still in development.