Question: 3ware and Raid 1

[Jesse]

Hi,

I will soon be installing a 3ware 9500-S12 card in my sage server. I would like to build two Raid 1 arrays using four 500gb hdd's. I will then be moving my sage recordings from the mish-mash of hdd's they are stored on onto the two Raid 1 arrays. Easy enough so far.

After this is all done it will be time for a fresh windows install. I will be installing windows using a couple of drives I previously used for recordings. These two drives will also be in a Raid 1 configuration.

Here is where I have questions. Would it be better to use the intel mobo's raid features with the two onboard sata connectors or the 3ware card for the windows install? Will the two Raid 1 arrays I set up to store recordings remain intact and recognizeable by the fresh windows install?

TIA

Jesse

[mattdcknsn]

Originally Posted by Jesse

Here is where I have questions. Would it be better to use the intel mobo's raid features with the two onboard sata connectors or the 3ware card for the windows install? Will the two Raid 1 arrays I set up to store recordings remain intact and recognizeable by the fresh windows install?
Jesse

I am not sure about your on board RAID controller but a lot of them are just software RAIDs. What is the make and model of the mobo?

The 3ware card is a good card (I have an 8000 series) which works very good. I am using it for storage. I would recommend the 3ware card for the storage only just because in the event of a mobo failure you can easily migrate the existing data array over to a new server. and at a later date if you want to upgrade the server its easier to move data on an external RAID card. If you use the on board controller it can get VERY messy.

To get the RAID array recognizable in the new system I would recommend removing the RAID card and installing the OS without it. This reduces the chance of blowing away the array (or having MS mess it up). Once the server is up make sure to install the same or newer drivers then it shouldn't have a problem recognizing the array.

[Jesse]

Hi,

Thanks for the help Matt.

My server mobo is an intel D865perl. Socket 478 and a few years old, but she has been rock solid reliable.

To get the RAID array recognizable in the new system I would recommend removing the RAID card and installing the OS without it. This reduces the chance of blowing away the array (or having MS mess it up). Once the server is up make sure to install the same or newer drivers then it shouldn't have a problem recognizing the array.

It is my usual practice, and my plan now, to install the OS without any peripherals installed, but I was unsure about the raid controller. Thanks for confirmation. I take your above statement to mean that the 3ware controller stores the actual array config info in its own memory which will remain intact from one windows install to the next. Is that correct?

Thanks again.

Jesse

[mattdcknsn]

Originally Posted by Jesse

I take your above statement to mean that the 3ware controller stores the actual array config info in its own memory which will remain intact from one windows install to the next. Is that correct?
Jesse

I actually dont know 100% that 3ware cards work like that. The last time that I migrated an array over to a new system with the 3ware cards it worked without a problem but I am hesitant to say it with complete accuracy.

One way to test this create the array and format it. then shut the server down, remove the card, boot it back up for a couple of minutes. Then shut it back down and install the card. If the drives are intact then it does.

I'll actually be doing the same thing this weekend. I migrated over to a new server and am going to be moving the 3ware card to a new mobo. I'll see if it works as well.

[mattdcknsn]

One other question. Why 2 single RAID 1s? The specs for that card say you can do a RAID 10. Then you could get better performance.

[dvd_maniac]

I take your above statement to mean that the 3ware controller stores the actual array config info in its own memory which will remain intact from one windows install to the next. Is that correct?

I believe the info is stored on the disks themselves.
I upgraded from 4*250GB drives to 4*400GB drives like so:
Started with 4*250GB drives in Raid-5 on a 3Ware 9500s-8 card in PC 1
Installed a second 3ware 9500s-8 on PC 2 and took out the 4*250GB drives from PC 1 and installed them in PC 2 using the new 3Ware card. The array was picked up by the card just fine.
However,

Once the server is up make sure to install the same or newer drivers then it shouldn't have a problem recognizing the array.

The PC 2 machine wouldn't boot into windows. I figured out after a massive headache that the driver and firmware need to match...

and go with Matt's suggestion on Raid-10

[stanger89]

Originally Posted by mattdcknsn

I actually dont know 100% that 3ware cards work like that. The last time that I migrated an array over to a new system with the 3ware cards it worked without a problem but I am hesitant to say it with complete accuracy.

Actually I believe 3ware stores the array config on the drives (perhaps in addition to the card). That allows the array to survive a move to a different (3ware) card.

Jesse, if I might ask, why aren't you planning on RAID-5 for the array? Two RAID-1 arrays seem like an aweful waste of space.

[Jesse]

Hi,

Thanks for all the info guys. I never thought about the config being on the drives themselves.

I have considered both Raid 5 and 10. Raid 10 looks quite good but it just does not look like it will scale so well. Wont I need four more drives to expand the array? Guess I should RTFM for the controller card....

I have gone back and forth about Raid 5. It has many advantages over 1 and 10. But the one thing I just cant get past is that it is all or nothing. If the array goes south for any reason then I loose it all. Don't want to try and explain that to the wife and kids.

Jesse

[stanger89]

Originally Posted by Jesse

I have gone back and forth about Raid 5. It has many advantages over 1 and 10. But the one thing I just cant get past is that it is all or nothing. If the array goes south for any reason then I loose it all. Don't want to try and explain that to the wife and kids.

What do you mean "array goes south"? RAID-5 will survive any single drive failure. Yes, more than that, and it's all gone. But if you lose more than 1 drive in a RAID-10 or 01 array, same thing happens.

[mattdcknsn]

Actually you can lose more than 1 drive in a RAID 10 as long as its the right drives. And make sure you do a RAID 10 not a RAID 01. There is a difference. I am using a RAID 5 at home for recordings and its been working great. I couldn't justify loosing half of my drives for recordings.

Originally Posted by stanger89

What do you mean "array goes south"? RAID-5 will survive any single drive failure. Yes, more than that, and it's all gone. But if you lose more than 1 drive in a RAID-10 or 01 array, same thing happens.

[stanger89]

Originally Posted by mattdcknsn

Actually you can lose more than 1 drive in a RAID 10 as long as its the right drives.

Well, yeah, but I guess the way I look at it is, if you can't guarantee survival of a multi-drive failure, the benefit is marginal, especially given the space cost. If you really need to survive a multi-drive failure, you should be looking at RAID-6.

And make sure you do a RAID 10 not a RAID 01. There is a difference.

Yeah, but I can never remember which is which.

[Jesse]

Hi Guys,

What do you mean "array goes south"? RAID-5 will survive any single drive failure. Yes, more than that, and it's all gone. But if you lose more than 1 drive in a RAID-10 or 01 array, same thing happens.

Are you aware of any other points of failure in a Raid 5 array than a disk failure? I am not being sarcastic here, I was under the impression that there was a possibility of corruption as well a problems due to power failures.

I know that with Raid 1 I could lose both discs and it is all gone. Not likely to happen. (...I know it is also unlikely that I would lose more than one disk at a time in a Raid 5 array...). If the controller takes a dive, or some other problem/failure arises that I have not considered then with Raid 1 I could still get the data off the disks.

Thanks again.

Jesse

[mattdcknsn]

I all depends on your comfort level. If you want maximum redundancy then 2 RAID 1s are better. If you can live with loosing half your drives.

With everything related to HDs there is always a possibility to data corruption due to power loss (with either a RAID 5 or 1). A RAID 1 works by writing data to one drive then writing it again to the other. If a power failure hits during the middle of a write then you have a RAID failure and have to figure out which drive is the correct one. Its not always the first one. But like you said you can always plug it into another computer and see whats on which drive.

stanger89: I had to correct you sorry. I was in an hour long debate with a guy at work about the differences between RAID 10 and 01. There isn't much difference until a problem creeps up, and you have to spend an extra 5 hours at the datacenter to figure it out.

[dvd_maniac]

If the controller takes a dive, or some other problem/failure arises that I have not considered then with Raid 1 I could still get the data off the disks.

Get a BBU for the controller. That should help with any power outage issues. And usually with a power outage during a write sequence the Array will just become degraded and you'll have to do a rebuild, which will not cause data lose. I've had this happen a few times already on my Raid-5(Lots of thunderstorms here in the N.E.). As far as a controller failure, you should be able to replace the controller and still have your data intact.
So I agree with Stanger... I would go with the Raid-5 if using 4 disks. Or for a little more money get a raid-6 card.

[stanger89]

Originally Posted by Jesse

Are you aware of any other points of failure in a Raid 5 array than a disk failure? I am not being sarcastic here, I was under the impression that there was a possibility of corruption as well a problems due to power failures.

Absolutely, RAID is protection against one thing and one thing only, disk failure, regardless of RAID level. I bring that up whenever somebody mentions RAID and Backup.

My point is, of the things that can take out an array (software, user, external factors, etc), the things that will take out a RAID-5 array but not a RAID-1 array, are among the most improbable of those events. I (personally) don't think that very marginal security gain justifies the sacrifice in storage efficiency and/or added cost of drives.

Originally Posted by mattdcknsn

I all depends on your comfort level. If you want maximum redundancy then 2 RAID 1s are better. If you can live with loosing half your drives.

I would probably argue then, that if you're uncomfortable with RAID-5 data security wise, you should avoid RAID all together.

With everything related to HDs there is always a possibility to data corruption due to power loss (with either a RAID 5 or 1). A RAID 1 works by writing data to one drive then writing it again to the other.

Actually I believe (HW RAID at least) that it writes to both simultaneously.

If a power failure hits during the middle of a write then you have a RAID failure and have to figure out which drive is the correct one. Its not always the first one. But like you said you can always plug it into another computer and see whats on which drive.

That would be why you have your PC on a UPS

stanger89: I had to correct you sorry. I was in an hour long debate with a guy at work about the differences between RAID 10 and 01. There isn't much difference until a problem creeps up, and you have to spend an extra 5 hours at the datacenter to figure it out.

No prob I make those sorts of corrections myself sometimes