[SierraDragon]

Originally Posted by misterdna 

...My only question is why not to boot from a RAID.
... a 4-drive single-volume RAID 5 array would be a very straight-forward set-up in the new Mac Pro, and I've read posts in various forums from people who are running this configuration. It seems like I could mirror the single-volume RAID regularly to an external drive (actually two externals, which would be rotated). It seems so simple...

But did you write it down with exact drives and usable capacities? A 4-drive array of any substantial capacity pretty much needs to be backed up to at least a 3-drive array; your "two externals, which would be rotated" turns out to be 2x3=6 drives. And system partitions typically need to be cloned, not just "backed up." You are now talking about lots of drives and complexity.

...I realize there are inherent complications and risks associated with RAIDs. I got the feeling from a recent post of yours that the OS is complicated and RAIDs are complicated, and its just asking for trouble to mix the two. Is it that simple? Is there evidence that this causes problems?...

Sorry, but

...It seems so simple...

and

...I realize there are inherent complications and risks associated with RAIDs.

are absolute contradictions in terms. Along with the need for multiple external drives, inherent complications and RISK are why I choose not to RAID my System drive. Once one writes it down and works out exact backup and recovery protocols the (IMO undesirable) complexity should be apparent.

I have said all along that given enough drives all kinds of RAID arrays including some that include the OS may make sense. Complexity is fully acceptable if enough drives are thrown at the data security issue. Personally I have high capacity needs and (except for offsite backup) I have no intention of throwing more drives at the problem than will fit in my MP; ergo for simplicity the System and apps will not be on a RAID array.

-Allen Wicks

[misterdna]

Originally Posted by mduell 

I'm not trying to be obtuse, I thought the risks of RAID were well known. Wikipedia has reasonable coverage of them.
The annoyance of losing the ability to boot your computer (for a time) because one or four drives failed is quite high in my book. Also should some part of the machine other than the RAID controller or a disk fail, you can't necessarily pull out the drives and stick them in another machine.

But if I regularly cloned a single-volume four-disk RAID 5 array to an external drive, seems like I could just boot from the external and be on my merry way without much down time (other than dealing with whatever was lost since the last back-up). And as time permits, I'd stabilize the RAID and clone to the RAID from the external. Am I being overly simplistic with this view?

Thanks for the link, I had not seen that page. I didn't find anything that addresses specific risks incurred in a system that boots from a RAID.

[misterdna]

Originally Posted by SierraDragon 

But did you write it down with exact drives and usable capacities? A 4-drive array of any substantial capacity pretty much needs to be backed up to at least a 3-drive array; your "two externals, which would be rotated" turns out to be 2x3=6 drives. And system partitions typically need to be cloned, not just "backed up." You are now talking about lots of drives and complexity.

Sorry, but and are absolute contradictions in terms. Along with the need for multiple external drives, inherent complications and RISK are why I choose not to RAID my System drive. Once one writes it down and works out exact backup and recovery protocols the (IMO undesirable) complexity should be apparent.

I have said all along that given enough drives all kinds of RAID arrays including some that include the OS may make sense. Complexity is fully acceptable if enough drives are thrown at the data security issue. Personally I have high capacity needs and (except for offsite backup) I have no intention of throwing more drives at the problem than will fit in my MP; ergo for simplicity the System and apps will not be on a RAID array.

-Allen Wicks

I see simplicity in a computer with a single volume. It's simple to define and interact with, even if it's complicated "under the hood" (such as with a four-drive RAID 5 scenario). Can you see why I see simplicity in that?

Speaking of simplicity, why can't I just clone my four-drive RAID 5 to an external 1TB drive nightly, using SuperDuper!'s smart-update? (actually, I'll rotate several externals). That seems very simple to me, no more complex than the non-RAID backup strategy I currently use (without a RAID). Note that the four drives are for speed rather than capacity, and I don't foresee needing a bigger external back-up (CLONE) drive in the foreseeable future.

If one of my RAID 5 drives goes down, no data is lost, as the three remaining drives contain all my data/apps/sys. If something uglier happens, I boot from my recently cloned external and I am good to go. Seems pretty simple to me.

Please tell me if you think I'm making a major error with my thinking.

Thanks,
Rob

[SierraDragon]

Originally Posted by misterdna 

But if I regularly cloned a single-volume four-disk RAID 5 array to an external drive...

Only be getting to operational detail can drive usage be rationally evaluated ("the devil is in the details..."). Please, write it down. For each drive: what nominal capacity and usable capacity, and the function of each of the 5 drives and whether internal or external and how connected. How and how often backup is to be done (e.g. Time Machine, Super Duper clone, Retrospect, whatever). Software or hardware based RAID control, and what brand.

-Allen Wicks

[misterdna]

Originally Posted by SierraDragon 

Only be getting to operational detail can drive usage be rationally evaluated ("the devil is in the details..."). Please, write it down. For each drive: what nominal capacity and usable capacity, and the function of each of the 5 drives and whether internal or external and how connected. How and how often backup is to be done (e.g. Time Machine, Super Duper clone, Retrospect, whatever). Software or hardware based RAID control, and what brand.

-Allen Wicks

Are you asking me to write it down on a piece of paper to be sure I have done appropriate planning before committing myself down a particular path?

Or are you asking me to post all these details on this thread so you can take the time to personally evaluate the system? If that's the case, I might as while write down all the systems I'm leaning towards, give you all the details of what I think I will be doing with the system, etc. etc. etc. But I doubt that will happen today, I've been here too much today, and am now behind on my work!

[SierraDragon]

Originally Posted by misterdna 

Are you asking me to write it down on a piece of paper to be sure I have done appropriate planning before committing myself down a particular path? Or are you asking me to post all these details on this thread so you can take the time to personally evaluate the system?

I just think your idea of what is simple may change when you get right down to it. Or maybe it really will be simple and some of us here will choose to emulate your proposed solution. Me, I am an anti-paper person. If you lay it out in a text file you can then copy and post it here for discussion. IMO going to the effort of writing all the details down for others to see is helpful - sort of online brainstorming.

-Allen Wicks

[OreoCookie]

Allen is right-on: without giving us specifics of what you need in terms of capacity, it's impossible to tell you whether a RAID (and what kind of RAID) is right for you.

In general, I think it's a good idea not to RAID the system drive (save for a RAID1, but that will give you only security in terms of drive failure!). The second thing is that your backup strategy is -- in any case -- way, way too naïve. Remember that cloning is a very, very bad way to back up your data! Any reasonable backup solution should give you the possibility to (i) restore old data and (ii) go back in time until you have a working system again. If you clone a borked drive, then your backup will be a borked system. Once you've cloned it, there is no way to go back to a working state!

This may not be important for things that don't change much (like backing up the system drive minus data!), but it certainly makes it useless as a sole backup strategy for your (fast changing) data. Also, keep in mind that your backup solution needs to have more capacity than the drives you're using, i. e. if you build a large RAID volume, you'll need an even larger one to back up to. Any storage solution has to include a proper backup solution.

So please post your requirements in details, including the following:
(i) Capacity needed now.
(ii) Growth of data per month or year.
(iii) Types of data with different priorities (e. g. scratch files don't need to be backed up as often or at all; is it video files, pictures, i. e. many small files or fewer larger files?).
(iv) Is there a lot of interdependency between your files or can you separate them into independent projects?
(v) Do you want to be/have to be able to access certain data all the time? If yes, what is their approximate amount (in GB) and growth over time?
(vi) Value of the different types of data.

Just to give you an idea: for larger, fewer files, seek times are less important than through-put. If you can separate your projects well, you can simply charge the customer for a harddrive and store his project on a dedicated harddrive.

[misterdna]

Originally Posted by OreoCookie 

Allen is right-on: without giving us specifics of what you need in terms of capacity, it's impossible to tell you whether a RAID (and what kind of RAID) is right for you.

I hate to say this, but I haven't really been asking you guys to tell me what type of RAID is right for me. I was really trying to learn why some of you said not to boot from a RAID, because a lot of you had said that as a matter of fact, but didn't explain why.

I participated in a few RAID-related threads here (maybe not enough for you guys to remember me?), asked some questions, had some recommendations made, etc. I will probably opt for one of the RAID set-ups that was presented and discussed by some of you. It didn't seem like I needed to present an idea that had already been discussed.

However, the one thing I didn't understand was simply, why everyone rejected the RAID boot idea immediately as if it were common knowledge that it's a really bad idea to boot from a RAID with their new Mac Pro. I never saw anyone say, "it's okay if you have the right backup scenario." No, all I saw was people saying you shouldn't boot from a RAID. Period.

So the details of "why" it is unequivocally a bad idea was what I wanted to know in my most recent posts, particularly since I have found users in other forums (apple, macrumors) who seem blissfully unaware of this edict, and happily are running their new Mac Pros with a single RAID 5 array (perhaps with high risk of impending doom?). Since the ideas for setting up a RAID in a new Mac Pro has been discussed in depth in this and other threads, I was trying to discuss the one thing I didn't see discussed (only stated) -- what are the reasons not to boot from RAID? Thus, my configurations of booting from a single-volume RAID 5 was put out there for the sake of general discussion, just to understand what the big problem with booting from a RAID setup like this is. I really was looking to learn in general terms, not get help from you in determining if this set-up was right for my situation.

Make sense?

Before I order my hardware, I will submit my intended set-up ideas (an details on how I use my system) to see what you guys think. Likely it will be a copy of one of the RAID configurations I've seen discussed already on this forum.

BTW, when I say "clone" I mean I use SuperDuper! to copy my drive to an external (actually two, that I rotate, so I can keep one off site). I do this so I will always have a bootable copy of my entire drive, so if anything happens to my drive (or my computer), I will always have complete data, apps, etc. and can be back up and working very quickly. Cloning my drive (if I'm using the right word) has saved my ass a couple of times, and I've never been told this is a bad idea. Obviously, it should not be the only backup method. I happen to also do incremental backups to REV drives and use Retrospect (running on an older computer) to copy my active jobs folder to another computer twice a day (each to a separate folder), and copy my entire user folder to another computer once a day. I also burn finished projects to DVD, and have kept most projects completed in the past couple of years on another drive. I feel I am probably overkilling it in the back-up department. But as far as my RAID 5 single-volume scenario being "cloned" (using SuperDuper!) sceneario, it was simply to address that, even if a RAID-boot mystery disaster occurred, it seemed like I would easily be able to recover. And I was hoping someone would address that particular scenario for my general learning, not to address it as the right solution to my particular needs.

Eek, I gotta limit myself to one less-wordy post a day, I'm getting behind on my work.

-R

[ninahagen]

So far I have been able to glean only five negatives to RAIDing the boot drive:

1) firmware update problems (referred to by mduell, but not fully explained)
2) inability to boot if any drive in the array goes down (an obvious fact)
3) a more pronounced need for external backup (but any pro should have it in any case)
4) the increased probabilty of array failure due to multiple HDs and a RAID controller (not much of an issue if backup is solid)
5) more complicated recovery protocol (yes, but I would never try to recover the system in order to reboot. With good backup data, you identify the failed HD, pull or replace it, sweep the rest, reinstall the system from the startup/utility disc, reconfigure your working drives and pull the data in from your backup.) Aside from reconfiguring your array, those are the same steps you would take working off a single HD for system, apps, scratch & data... a little more complicated sure, but if you are even attempting a RAID, you have to be ready for that level.

There may be more I don't know of, but those do not seem that daunting.

If that's the sum of the issues, RAIDing the boot drive seems like a good way to gain extra internal HD capacity and the simplicity of a single volume, since you don't have to dedicate a bay and an HD to system & apps.

[misterdna]

Originally Posted by ninahagen 

So far I have been able to glean only five negatives to RAIDing the boot drive:

1) firmware update problems (referred to by mduell, but not fully explained)
2) inability to boot if any drive in the array goes down (an obvious fact)
3) a more pronounced need for external backup (but any pro should have it in any case)
4) the increased probabilty of array failure due to multiple HDs and a RAID controller (not much of an issue if backup is solid)
5) more complicated recovery protocol (yes, but I would never try to recover the system in order to reboot. With good backup data, you identify the failed HD, pull or replace it, sweep the rest, reinstall the system from the startup/utility disc, reconfigure your working drives and pull the data in from your backup.) Aside from reconfiguring your array, those are the same steps you would take working off a single HD for system, apps, scratch & data... a little more complicated sure, but if you are even attempting a RAID, you have to be ready for that level.

There may be more I don't know of, but those do not seem that daunting.

If that's the sum of the issues, RAIDing the boot drive seems like a good way to gain extra internal HD capacity and the simplicity of a single volume, since you don't have to dedicate a bay and an HD to system & apps.

Thank you, thank you, thank you! I guess I haven't been taking crazy pills. This is directly answering the question I had asked. And your conclusions seem generally on par with my own, which gives me some faith in my own powers of research and reasoning... Do any of you think Nina is missing something?

Thanks again!

[ninahagen]

Just thought of one more potential negative and one more question:

— sierradragon told us that the speed advantages of RAID are optimized at 50% or less of the nominal capacity. Is that unique to RAID arrays? Don't standard single drives have speed differences between optimal and nomimal data loads. I have always just used 60%~70% of nominal capacity as a rule of thumb. If say a normal HD were OK up 2/3 of nominal capacity, and a RAID were only OK up to half, your boot volume/stripe would have to be proportionally bigger.

— question: if misterdna head straight off a cliff and do boot from a RAID volume, is it better to make a formal partition of the volume for Leopard, and if so, how big to keep it running snappy?

[mduell]

Originally Posted by ninahagen 

So far I have been able to glean only five negatives to RAIDing the boot drive:

To that I'd add: More chance of problems after an abrupt power outage (without UPS, after UPS is exhausted, when the powersupply goes up in smoke, etc) due to write caching and the lack of atomicity.

Originally Posted by ninahagen 

Just thought of one more potential negative and one more question:

— sierradragon told us that the speed advantages of RAID are optimized at 50% or less of the nominal capacity. Is that unique to RAID arrays? Don't standard single drives have speed differences between optimal and nomimal data loads. I have always just used 60%~70% of nominal capacity as a rule of thumb. If say a normal HD were OK up 2/3 of nominal capacity, and a RAID were only OK up to half, your boot volume/stripe would have to be proportionally bigger.

— question: if misterdna head straight off a cliff and do boot from a RAID volume, is it better to make a formal partition of the volume for Leopard, and if so, how big to keep it running snappy?

The performance curve of a RAID array depends strongly on the RAID level and the controller. It can be flatter or steeper than a typical single drive.

If you're only going to have one array, why bother with more than one volume?

[misterdna]

Originally Posted by mduell 

To that I'd add: More chance of problems after an abrupt power outage (without UPS, after UPS is exhausted, when the powersupply goes up in smoke, etc) due to write caching and the lack of atomicity.

Interesting point, particularly with a software RAID. The wikipedia RAID page says that both these power outage issues are addressed in a hardware RAID: "Most hardware implementations provide a read/write cache which, depending on the I/O workload, will improve performance. In most systems write cache may be non-volatile (e.g. battery-protected), so pending writes are not lost on a power failure." The Mac Pro Raid Card has a 72 hour battery.

And in regards to atomicity, wikipedia mentions: "While the battery-backed write cache may partially solve the problem, it is applicable only to a power failure scenario."

Obviously, the RAID card back-up is not a guarantee that the RAID won't be corrupted due to power failure. But taking a step back, aren't the issues you mention related to all RAIDs, not just when booting from a RAID? Or do you see a synergy that occurs when RAIDing the boot drive that intensifies the risks you mention?

Bottom line is, I'm still not seeing why a RAIDed boot drive going down is of much more consequence than a RAIDed data drive going down. Either way, you reset the RAID (replacing drives if necessary) then clone from your backup. So what puzzles me is, I haven't heard people saying "don't RAID a data drive," but I've certainly heard "don't RAID a boot drive." I still don't think there's been information provided that makes one seem so very much worse than the other. But I'm still all ears...

I genuinely appreciate the indulgence in this subject -- it was worth whining about in a few post to finally get the discussion going. I will have to join the other forums just to reference this discussion to others who had the same question I did.

[mduell]

The battery on the cache helps, but it's no silver bullet. The life of the battery degrades over time, power outages last longer than the battery runtime, people don't necessarily return to their computers immediately to turn them on, etc.

The difference between your boot volume and your data volume is that you can work without your data volume.

[misterdna]

Originally Posted by mduell 

The difference between your boot volume and your data volume is that you can work without your data volume.

If my data is gone, I'm screwed. The computer not booting isn't the end of the world for me, I have other computers I can always work from. So as long as I have a functional backup, the difference between losing the boot & data vs. just the data doesn't seem like a huge deal in my case.

Anyway, I do thank you again for helping me understand the negatives of this option. While the headaches and risks of booting from a RAID don't seem as terrible as I expected, I understand why people tend to prefer booting from a dedicated drive. And now that I feel I understand the negatives, I can try to assess the positives and then decide if a single volume RAID 5 configuration is worth considering.

All comments (even those that I said were off the topic I was pursuing) have been instructional -- it's amazing to have access to so much knowledge and advice.

-Rob

[SierraDragon]

Originally Posted by misterdna 

So as long as I have a functional backup, the difference between losing the boot & data vs. just the data doesn't seem like a huge deal in my case.

Except that OS and data on the same array can facilitate a scenario where all is lost including the backup.

Originally Posted by misterdna 

I hate to say this, but I haven't really been asking you guys to tell me what type of RAID is right for me. I was really trying to learn why some of you said not to boot from a RAID.

Sorry, but you are not paying attention. You say you have done your homework (e.g. Wiki on RAID) but the statements above say otherwise. All RAID arrays are not the same and are totally situation-dependent! The issues you raise are not simply about RAID per se.

Thus, my configurations of booting from a single-volume RAID 5 was put out there for the sake of general discussion, just to understand what the big problem with booting from a RAID setup like this is. I really was looking to learn in general terms, not get help from you in determining if this set-up was right for my situation. Make sense?

NO it does not make sense because "your situation" has not been specified. How many times must I say write it down, the devil is in the details, etc.? "RAID" means redundant array of independent drives. Some arrays in some scenarios are appropriate. Other arrays in different scenarios are inappropriate. Like I have repeatedly said, it is all about the specifics. Without specifics "now that I feel I understand the negatives" is not happening even if you think it is. Ongoing generic discussion is ludicrous, you can get that from Wiki; until you lay out specifics (previously described) I for one am done commenting.

-Allen Wicks

[misterdna]

Originally Posted by SierraDragon 

Sorry, but you are not paying attention. You say you have done your homework (e.g. Wiki on RAID) but the statement above says otherwise. All RAID arrays are not the same and are totally situation-dependent! The issues you raise are not simply about RAID per se.

NO it does not make sense. How many times must I say write it down, the devil is in the details, etc.? "RAID" means redundant array of independent drives. Some arrays in some scenarios are appropriate. Other arrays in different scenarios are inappropriate. Like I have repeatedly said, it is all about the specifics. Ongoing generic discussion is ludicrous; until you lay out specifics (previously described) I for one am done commenting.

-Allen Wicks

Sorry Allen, but while I typically get so much from your posts, the past few days the tone of the discussion between you and me has felt argumentative, and I'm just not here to argue with anyone.

I have wanted to understand a basic tenant that has been thrown around the Mac Pro RAID discussions, and I feel I have now achieved the better understanding I was searching for. I am not quite sure why my approach appears to rub you the wrong way, but quite frankly, I feel slightly attacked by your insistence that I'm not paying attention, and by your calling my approach to learning "ludicrous."

I'm simply trying to coming to my own understanding of all the posts I'm reading before getting to the details of configuring my system... And if I'm going to be attacked, probably best for me to steer clear of posting much else on this board, and just make my own judgments based largely on posts on this board (many of them being your posts).