Considering SSD software RAID0...

[AppleWorking]

My boot time right now from power button to usable desktop is extremely fast with a single X25-M SSD... I was wondering if setting up a software RAID0 of two SSDs would result in a longer boot time? I mean, does it take a long time for the software RAID0 to initialize on boot up? If it will cause me to have a slower boot time because of this "initialization" then I think I'll leave well enough alone. I would hate for my boot time to be twice as long, or even a little longer...

I also noticed a member here (VR) had this to say about SSD Raid0...

The bottom line is that RAID0 arrays of SSD's will not have a huge advantage in terms of every day performance because with such a large stripe size, you don't benefit from the added parallelism for small read/write operations. The key compelling reason to RAID SSD's is to combine small drives into a larger more practical volume size... not for performance although you will see added performance on sustained transfers of larger files.

This makes me believe that a SSD Raid0 really has no "holy cow" speed increase in regard to everyday use, except when it comes to large file transfers.

So, if a RAID0 of two SSDs will cause me to have a longer boot time, and it doesn't even provide a large increase in performance except in large file transfer situations, then it looks like I will save my money and forget the SSD RAID0 idea (provided all of this info is correct, I dunno).

Anyone have any thoughts on this? Thanks.

 

[TheStrudel]

You could use a smaller stripe size. It's an option. I don't know about longer RAID-induced initialization, but in theory if you're using an extremely small stripe, or block...you'd reap more benefit, wouldn't you?

I don't think your boot time will get longer, But I do agree with VirtualRain that your speed increase won't be a linear doubling of the single SSD's speed.

Sound reasonable?

 

[Tesselator]

I think it might be close to the same but I dunno for sure. With two the system has to load & initialize two units then read the stripe info from both and mount the volume. Maybe this takes 3 to 5 seconds and I guess the SSD RAID0 once mounted will be pretty close to about that much faster for booting. So it breaks even? Or not... That's just a guess. Most of the speed increase you get from booting off of SSDs is due to the low access times (latency). I guess that doesn't change too much between SSD and 2-SSD-RAID0.

I think OS X 10.5.8 reads about 1.5GB to 2GB (total data) from the drive/s before it's completely finished and all settled down. How much faster is a 2-SSD-RAID0 volume over a single SSD?

It writes a bunch too but I dunno how much. 200 MB? No idea.


What are your boot times now? Mine is currently taking 11 seconds for the grey blanket + grey apple. And another 12 seconds for it to load OS X, log-in and load about 12 to 15 start-up apps. I currently get between 21 and 24 seconds from power button push to fully loaded and waiting for clicks. Is an SSD much faster?

Another question I have is: Exactly how important is this booting time thing? I boot my machine about once a week. So that's 24 seconds a week or about 2 minutes a month. To me twice that or eliminating it all together (0 boot times) is worth about one saltine cracker (with butter) and not much more. Now, on a laptop (where SSDs shine the brightest anyway) it's worth much more! Even approaching the actual price of an SSD drive. When I was using Laptops for work (Teaching Uni) I booted up 5 to 10 times a day and slept the machine another 10 or 15 times a day. Many boots were during a conversation that pended on pertinent information on the laptop or on the net. Waiting 20 seconds for a boot in the middle of a conversation it too much to ask.

 

[TheStrudel]

For my part, I would say frequent seek hangs when using pro apps are the real reason. Boot time is icing on the cake.

 

[gugucom]

I havn't done any comparisons but I have been booting with a dual SSD SW RAID0 for some weeks now. It is blindingly quick. So I cannot believe that it adds time to a single SSD setup. But taking the array apart just to measure it exceeds my curiosity. Just take my word that it is not slow!

 

[AppleWorking]

Thanks for the replies. My MP right now as it is boots in about 30 sec from power button to usable desktop. I have to reboot into windows quite often thus the question. I've seen a few threads around here where peeps are complaining about a slower boot time ever since implementing a software RAID. They say it's initializing. Made me wonder... Any slower on boot and I would prefer just to leave things as is...

 

[VirtualRain]

Many things to add here...

Boot is not just loading a bunch of stuff off disk into memory, there's also a lot code execution that needs to happen and dependencies on other devices in your system (getting an IP address via DHCP is just one example, but there are a ton of other hardware initializations that occur). All of these things will throttle boot to some extent. Like the old saying goes... 9 women can't have a baby in 1 month... the same applies to optimizing boot performance... after a certain point, the boot process is not constrained by storage speed. Where is this point?... a single SSD, or two or three in RAID0? I'm not sure. I'm guessing that after a single top-shelf SSD, diminishing returns set in fairly quickly. Even the 24 SSD array experiment I saw on YouTube didn't boot much faster than my system.

Despite my own assertion that it doesn't add much performance, I run dual SSD's in software RAID0. I did this primarily for the benefits of a single larger volume but there may be some circumstances where I'm getting a performance boost. I certainly don't think it hurts.

Finally, you could use a smaller stripe which will boost read performance, but it can quickly kill write performance with the write-erase block penalty that comes with writing to MLC flash. Consider that on a used drive, writing just 4K of data might require an entire 512K page to be rewritten in flash. If you were using 4K stripes and had to write just 16K of data, you would effectively incur 4 write-erase penalties and 2MB of data would have been moved around in flash instead of just the 16K you needed to commit to disk.

So my advice is to just f'n give er! Go for it! But don't expect a doubling of performance or anything even close.

 

[Tesselator]

I havn't done any comparisons but I have been booting with a dual SSD SW RAID0 for some weeks now. It is blindingly quick.

How many seconds?

Thanks for the replies. My MP right now as it is boots in about 30 sec from power button to usable desktop.

So just a little slower than mine with no SSD at all. I'm going to take a stab and say a second SSD will not offer a noticeable increase.

 

[AppleWorking]

So my advice is to just f'n give er!

Hey, there you are. Okay, so I'll just f'n give er. LOL And if you buy my second processor I can f'n give er real soon.






















I wish I knew what "f'n give er" meant. lol

 

[VirtualRain]

I wish I knew what "f'n give er" meant. lol

You gotta watch the movie Fubar to know where this comes from! It's a Canadian classic!!!

 

[AppleWorking]

You gotta watch the movie Fubar to know where this comes from! It's a Canadian classic!!!

Okay, gotcha.

 

[Gav2k]

Couple of things you need to look at really. What's your hard drive controllers make and model. Find this out check it's throughput and look what your getting from your ssd. Just thinking it's sata300 won't do.

Secondly software based raid adds CPU cycles as the CPU had to deal with all data requests not a hardware chip. So you need to factor in things like additional heat and noise. Not to mention possible lag from CPU intensive apps due to the CPU being needed else where.

 

[gugucom]

How many seconds?

Probably 6 s EFI and 1 s for OS X. But I'm estimating by historic values. I'm putting a RAID card in which is taking much longer to go up in EFI. I'm also working on the Vista array, so I cannot have the SW OS X array in the Mac Pro.

One thing is for sure. RAID cards add a lot to boot and shut down time.

 

[nanofrog]

Probably 6 s EFI and 1 s for OS X. But I'm estimating by historic values. I'm putting a RAID card in which is taking much longer to go up in EFI. I'm also working on the Vista array, so I cannot have the SW OS X array in the Mac Pro.

One thing is for sure. RAID cards add a lot to boot and shut down time.

Boot yes, shutdown, not that I've ever noticed with the Areca's. I've not had any problems with it. The slowest it gets, has to do with Windows Updates occuring once the Shutdown or Restart sequence has started.

 

[gugucom]

Boot yes, shutdown, not that I've ever noticed with the Areca's. I've not had any problems with it. The slowest it gets, has to do with Windows Updates occuring once the Shutdown or Restart sequence has started.

I get something like 2-3 minutes or more in OS X and almost instant in Vista. Previously my OS X shut down in seconds.

Edit: I measured and it is more like 50-70 s.

 

[fernande-mac]

I wish I knew what "f'n give er" meant. lol

1. give'r
Function: Verb
Etymology: Canadian, particular to rural areas, especially Lanark County Ontario and most of Alberta; An amalgam of the words give and her; made popular by movie "FUBAR"
1. Going all out and/or balls to the wall to take care of business as quickly and as awesomely as possible
2. Acting in a way that is like you're rocking out really hard, but at the same time, trying to solve a problem that may or may not involve drop-kicking something without hesitation

When you're trying to get your politics paper done before the office closes and plan how you're going to get drunk later on that night, and you've only got 45 minutes left to figure out both problems, and you're so pumped up that you might drop-kick your roommate because he ate all of your peanut butter - you just give'r!

 

[ungraphic]

A simple question:

Does the software RAID0 setup with either SSDs or HDDs hamper the CPUs full performance? I've been told it eats up a bit of CPUs power......if so, does having a RAID card (that costs hundreds extra) really give a significant boost?

 

[nanofrog]

I get something like 2-3 minutes or more in OS X and almost instant in Vista. Previously my OS X shut down in seconds.

That seems really messed up to me.

Let me send off a few emails, and see what I get back on it. I just hope I can find someone else with an '06 model.

 

[nanofrog]

A simple question:

Does the software RAID0 setup with either SSDs or HDDs hamper the CPUs full performance? I've been told it eats up a bit of CPUs power......if so, does having a RAID card (that costs hundreds extra) really give a significant boost?

Not with RAID0, and the limit of drives capable of being run by the system (SATA ports on the board). Parity based RAID is another story, even on smaller drive quantities, but not impossible to do provided the software support is there (not in a MP though).

You could do it with a separate SATA card and it's drivers (won't boot).

 

[Macinposh]

Secondly software based raid adds CPU cycles as the CPU had to deal with all data requests not a hardware chip.

The cpu useage should not be an real issue,as it is very small. Remeber seeing some charts with 0.5-1.5% useage during heavy loading.

've seen a few threads around here where peeps are complaining about a slower boot time ever since implementing a software RAID. They say it's initializing.

When I had raid10 under tiger it normally booted extremely quickly. Boot times were around 10-15s. But when I had had the system up and running for weeks,sleep bug mad me restart or there were some power failures,then the bootup times went down the *******. They were around 2 minutes or something.

Now that leopard messed up my raid array (can read/write but can not boot from it!) I have had to resort to boot from the internal sata,wich takes about a 1 1/2 minutes or so. It sucks.

 

[AppleWorking]

1. Going all out and/or balls to the wall to take care of business as quickly and as awesomely as possible

I like that

2. Acting in a way that is like you're rocking out really hard, but at the same time, trying to solve a problem that may or may not involve drop-kicking Tesselator without hesitation

LOL That's a good one!



kidding

 

[Dreamail]

A bit off topic but somehow related:
I always wondered how software RAID 0 SSD boot drives cope with system crashes or power loss.

Mac OS X is quite stable, but once in a while things just hang. Photoshop is a good candidate or Flash in Safari.
In theory only the app should hang, but often I find the whole Mac Pro is gone and pressing the front button for a forced shutdown is the only way to regain control.

Same goes for sudden power losses where the Mac just goes off.


I wonder how a software RAID 0 striped boot drive will handle these scenario.
Surely at that point some files are half-written and corrupted.
What's your experience with such situations?
If the striped boot volume gets corrupted do you have to re-format the SSD and re-install from a backup?

 

[ungraphic]

A bit off topic but somehow related:
I always wondered how software RAID 0 SSD boot drives cope with system crashes or power loss.

Mac OS X is quite stable, but once in a while things just hang. Photoshop is a good candidate or Flash in Safari.
In theory only the app should hang, but often I find the whole Mac Pro is gone and pressing the front button for a forced shutdown is the only way to regain control.

Same goes for sudden power losses where the Mac just goes off.


I wonder how a software RAID 0 striped boot drive will handle these scenario.
Surely at that point some files are half-written and corrupted.
What's your experience with such situations?
If the striped boot volume gets corrupted do you have to re-format the SSD and re-install from a backup?

From my own HDD RAID0 setup, i've had some crashes, but not many. In the two years i've had my RAID0 setup with two 250gb Western Digitals, I havent noticed any problems with Software raid, even after improper shutdowns.

 

[Tesselator]

Well, it's the same as with single drives. If the drives are writing during the crash or black-out then there will be a splat file somewhere. Some drives and OS's can know about such things and verify/erase the splat file(s) and some can't. In either case when that happens the user needs to use the Disk Utility "Repair" functions or those from some 3rd party software and scan the FAT/BAM/Whatever and the surfaces. If you're in a state that uses the fake "rolling brown outs" as a way to justify price hikes then you need to get yourself a UPS with line conditioning as the trailing edge of a power-out is pretty dangerous for computers. Imagine turning up the voltage from 114 to near 200 momentarily just before dropping it to 0 and then often bouncing it up and down once more the power zero condition. Definitely not good for your system.

The information that controls/links the various members of a RAID0 in Mac OS / Firmware is written to a hidden partition and AFAIK is only accessed during system startup or when the RAID is being created the first time. So no crash is going to blow away of the members' relationships leaving your RAID inoperable.

 

[nanofrog]

Well, it's the same as with single drives.

Exactly. No drive setup is immune.

If the drives are writing during the crash or black-out then there will be a splat file somewhere. Some drives and OS's can know about such things and verify/erase the splat file(s) and some can't. In either case when that happens the user needs to use the Disk Utility "Repair" functions or those from some 3rd party software and scan the FAT/BAM/Whatever and the surfaces.

Most of the time, the OS can try to fix itself automatically, or might require a little user intervention (warning notices, "Run .... to diagnose/fix sort of thing). But not always (Kernel corruption for example).

Most of the applications (data being written during the failure) will require some user intervention at a minimum, if not a complete recreation, depending on the apps ability to assist in recovery (i.e. auto saves help reduce the amount of work to be recreated).

...the trailing edge of a power-out is pretty dangerous for computers. Imagine turning up the voltage from 114 to near 200 momentarily just before dropping it to 0 and then often bouncing it up and down once more the power zero condition. Definitely not good for your system.

Yep. Fortunately, most UPS's are up to the task for this.

The information that controls/links the various members of a RAID0 in Mac OS / Firmware is written to a hidden partition and AFAIK is only accessed during system startup or when the RAID is being created the first time. So no crash is going to blow away of the members' relationships leaving your RAID inoperable.

In the case of GUID partition tables, it's duplicated on both the front and back of the disk. So it has a duplicate, which helps in the event damage does occur. It offers the ability to salvage the drive, and access the data on it.