Can you stripe together 2 striped sets?

**ryandinan** · 07-08-2003, 11:38 AM

Ok...let me see if I can make this more clear...

I have four (4) 240GB Maxtor drives. I wanted to create one strip set including all four drives, and be done with it.

However, the Si raid controller card didn't like having all four drives in one set (I guess it was a size issue, since this is close to 1TB). So, I had to break them up into 2 stripe sets (each having 2 drives) in order to get it to work.

Now, in Win2K, I went to device manager to see what I could do with these two striped sets. For simplicity, we'd like to have these 2 sets appear as a single volume - hence the orignial plan of just striping all 4 drives together in one set.
In disk manamgement, I had the option of spanning the two stripe sets together, as well as striping the two stripe sets together.

I didn't realize you could - or think anybody would want to - stripe together multiple stripe sets.

How would that actually work anyway? Would half the data get written to one 'stripe set' and the other half get written to the other set? - and since data is being written to a stripe set - would that data be split in half again across the two drives in the set?? This is making my nose bleed...

If the above is indeed what occurs, is this essentially what would happen if I simply had all 4 drives in one stripe set? In other words, does the data get split up based on how many drives you have in the array? For example, 4 drives would mean that 1/4 the data is written to each drive - 6 drives would be 1/6, etc, etc.?

I understand that the way this is configured, I'd have two striped arrays in hardware (on the Si RAID controller card) - and if I were to select the option to stripe these two arrays together, I'd also be including a software-controlled array (in Win2k).

I chose the span option (as that made more sense at the time) - but I have no problems going back and changing this if there are benifits to striping these two striped sets together

Thanks for clearing this up for me!

-Ryan

**OS-Wiz** · 07-08-2003, 01:48 PM

First off, software RAID of any flavor isn't a good thing. Second, are you using a 4 or 2 port RAID controller? If its a 4 port controller, do a 10 array; else just do the 2, 2 HD arrays.

**pudad** · 07-08-2003, 01:53 PM

you want to do this w/ crappy ata drives? that is just asking for problems.

**ryandinan** · 07-08-2003, 02:00 PM

Originally posted by OS-Wiz
First off, software RAID of any flavor isn't a good thing. Second, are you using a 4 or 2 port RAID controller? If its a 4 port controller, do a 10 array; else just do the 2, 2 HD arrays.

It's a 2 port controller.
Besides, we need all the space, so a 10 array wouldn't fit the bill..
But anyway - was spanning these two striped sets the best way to go?
And I know that software RAID is not the best due to all the cpu cycles it takes up, but this machine is really nothing but a storage array.

pudad:

I always thought that ATA drives were the idea behind RAID (redundant array of inexpensive disks). Using SCSI drives for this application would be cost prohibitive for our needs. Besides - the quality/reliability of ATA drives are very good in comparison.
In fact, we just had a SCSI drive go down in our file server the other day...
All of our IDE RAIDs have never had a problem to date (knock on wood).

-Ryan

**pudad** · 07-08-2003, 03:05 PM

Originally posted by ryandinan

It's a 2 port controller.
Besides, we need all the space, so a 10 array wouldn't fit the bill..
But anyway - was spanning these two striped sets the best way to go?
And I know that software RAID is not the best due to all the cpu cycles it takes up, but this machine is really nothing but a storage array.

pudad:

I always thought that ATA drives were the idea behind RAID (redundant array of inexpensive disks). Using SCSI drives for this application would be cost prohibitive for our needs. Besides - the quality/reliability of ATA drives are very good in comparison.
In fact, we just had a SCSI drive go down in our file server the other day...
All of our IDE RAIDs have never had a problem to date (knock on wood).

-Ryan

Yeah I have a hard time believing that, what kind of drives was it? How old? And SCSI raid came before this ide raid ...

RAID == redundant array of independent disks

Raid1 is fine for ide, but raid0 is just too risky, ide drives are just too flaky. Adn this idea you have is ecven worse. Statistically a raid0 array doubles the chances of problems, what you are suggesting quadruples it!!!

**pudad** · 07-08-2003, 03:07 PM

hmm, I am betting that scsi drive was much older than your ide raid arrays simply because ide raid is a much newer technology than scsi.

**ryandinan** · 07-09-2003, 12:19 AM

Originally posted by pudad

Yeah I have a hard time believing that, what kind of drives was it? How old? And SCSI raid came before this ide raid ...

RAID == redundant array of independent disks

Raid1 is fine for ide, but raid0 is just too risky, ide drives are just too flaky. Adn this idea you have is ecven worse. Statistically a raid0 array doubles the chances of problems, what you are suggesting quadruples it!!!

The RAID acronym I used was the original definition - it has since been changed to "independant"

.

I'm just trying to figure out if spanning the 2 stripe sets was better than striping together the 2 stripe sets. I have to do one of those options.

BTW - the SCSI drive in the array that failed was 3 years old. We still have IDE Media raid's working daily (as video capture scratch disks) that are older.

I think IDE drives have come a long way, and are no longer the flaky beasts they used to be..

-Ryan

**pudad** · 07-09-2003, 12:56 AM

Originally posted by ryandinan

The RAID acronym I used was the original definition - it has since been changed to "independant" .

I'm just trying to figure out if spanning the 2 stripe sets was better than striping together the 2 stripe sets. I have to do one of those options.

BTW - the SCSI drive in the array that failed was 3 years old. We still have IDE Media raid's working daily (as video capture scratch disks) that are older.

I think IDE drives have come a long way, and are no longer the flaky beasts they used to be..

-Ryan

hmm yeah ide is a lot better now. 3 years eh, what is the waranty? I wonder why it is "inexpensive"?

hmm, strping the stripe, do you really need that much throughput? I'd just go w/ 2 sripes...

**SkyDog** · 07-09-2003, 09:18 AM

Originally posted by ryandinan
I think IDE drives have come a long way, and are no longer the flaky beasts they used to be..

Actually, I remember looking at some MTBF ratings on some IDE hard drives and seem to remember the newer ones being lower than previous ones. And some of those newer MTBF ratings are specifying that the drives be used only X number of hours per day! I wouldn't count on newer IDE drives being any more durable than their predecessors, and none of them are anywhere close to the reliability of SCSI drives in general. If they were much more reliable, then why would all the major hard drive manufacturers be cutting most of their warranty lengths from 3 years to 1 year?

Originally posted by ryandinan
I always thought that ATA drives were the idea behind RAID (redundant array of inexpensive disks). Using SCSI drives for this application would be cost prohibitive for our needs. Besides - the quality/reliability of ATA drives are very good in comparison.
In fact, we just had a SCSI drive go down in our file server the other day...
All of our IDE RAIDs have never had a problem to date (knock on wood).

The RAID acronym has been used to refer to "inexpensive" disks, but that's not necessarily meant to refer to IDE/ATA. The idea is that smaller, slower disks can be used in place of larger, faster disks to achieve the same type of throughput and potentially better reliability. Those smaller, slower disks that comprise an array would be very inexpensive in comparison to the mammoth single drives they could be compared to.

As for your SCSI array failing while the ATA ones haven't... Let's just say you're bucking the odds. Seagate's good about posting their MTBF ratings on their web site, so let's take a quick look at a couple of randomly selected recent drives:

ST3120022A Barracuda ATA 7200 RPM 120 GB: 600,000 power-on hours
ST173404LW Cheetah SCSI 10000 RPM 73 GB: 1,200,000 power-on hours

So the average ATA drive is expected to die twice as fast as the average SCSI drive under normal usage conditions. And that's before taking into consideration that the documentation states that the SCSI drive's MTBF numbers were built on the assumption that the SCSI drives' "normal usage" consists of 720 operating hours per month. If you do the math, 720 hours works out to 30 days, meaning they're designed to run 24/7.

**pudad** · 07-09-2003, 09:32 AM

Originally posted by SkyDog

Actually, I remember looking at some MTBF ratings on some IDE hard drives and seem to remember the newer ones being lower than previous ones. And some of those newer MTBF ratings are specifying that the drives be used only X number of hours per day! I wouldn't count on newer IDE drives being any more durable than their predecessors, and none of them are anywhere close to the reliability of SCSI drives in general. If they were much more reliable, then why would all the major hard drive manufacturers be cutting most of their warranty lengths from 3 years to 1 year?

The RAID acronym has been used to refer to "inexpensive" disks, but that's not necessarily meant to refer to IDE/ATA. The idea is that smaller, slower disks can be used in place of larger, faster disks to achieve the same type of throughput and potentially better reliability. Those smaller, slower disks that comprise an array would be very inexpensive in comparison to the mammoth single drives they could be compared to.

As for your SCSI array failing while the ATA ones haven't... Let's just say you're bucking the odds. Seagate's good about posting their MTBF ratings on their web site, so let's take a quick look at a couple of randomly selected recent drives:

ST3120022A Barracuda ATA 7200 RPM 120 GB: 600,000 power-on hours
ST173404LW Cheetah SCSI 10000 RPM 73 GB: 1,200,000 power-on hours

So the average ATA drive is expected to die twice as fast as the average SCSI drive under normal usage conditions. And that's before taking into consideration that the documentation states that the SCSI drive's MTBF numbers were built on the assumption that the SCSI drives' "normal usage" consists of 720 operating hours per month. If you do the math, 720 hours works out to 30 days, meaning they're designed to run 24/7.

(read my mind)

Very nice skydog!

hmm, I thought initially raid was a thing mainly for stripping and data protection stuff because any drives back in the day were flaky as heck...

**ua549** · 07-09-2003, 09:58 AM

If having all the storage appear as a single volume is your goal, you can simply mount the second volume in an empty directory on the first volume. Not only that, the second volume can be accessed by its own drive letter or via the mount point on the first volume.

Use disk manager or commandline diskpart.exe to set it up.

**pudad** · 07-09-2003, 10:11 AM

Originally posted by ua549
If having all the storage appear as a single volume is your goal, you can simply mount the second volume in an empty directory on the first volume. Not only that, the second volume can be accessed by its own drive letter or via the mount point on the first volume.

Use disk manager or commandline diskpart.exe to set it up.

very very nice!

**ua549** · 07-09-2003, 10:24 AM

Just another little used feature of Win2k and later.

**pudad** · 07-09-2003, 10:28 AM

Originally posted by ua549
Just another little used feature of Win2k and later.

cool, maybe I will stop bashing it now

**vertices** · 07-09-2003, 11:49 AM

Wouldn't another logical "cheap" method here be to just set up all 4 disks as independent disks on the hardware raid controller and then just RAID 5 them through Windows Server?

You would still get speed enhancements, but better yet, if one drive goes down you don't lose everything.

Thats what I would do in that situation.

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