Windows' Raid 5

[imported_goku]

Ok, I know that software raid 5 is significantly slower than with a dedicated hardware controller but I had the folowing questions.
1. Is software raid more reliable than having a controller card?
2. If your software raid were to fail (lets say 2000 got fubared) so you reinstalled windows 2000, are you able to recover the array?

 

[jondercik]

1. No
2. No

 

[nweaver]

windows has crappy S/W Raid, as opposed to Linux, where S/W raid is pretty good.

 

[Jon855]

3Ware makes one of the best RAID 5 cards on the market

 

[ITJunkie]

Originally posted by: jondercik
1. No
2. No

:thumbsup:

 

[bsobel]

1. Is software raid more reliable than having a controller card?

No it would not be more reliable.

2. If your software raid were to fail (lets say 2000 got fubared) so you reinstalled windows 2000, are you able to recover the array?

If your asking if say the OS itself got hosed and you had to reinstall, then yes, you can remount the raid volume.

Bill

 

[Smilin]

1. Yes
2. Yes

1. Hardware raid doesn't fail as gracefully as software. I've seen numerous times where a failed drive will wreck the parity information across all drives in an array leaving you with 3 or more useless drives instead of just one. When a drive fails in software raid it either fails gracefully or the OS goes down at the same time preventing junk data from being written to the other drives. It sounds odd but once you've seen enough failures you'll spot the trend as well (When doing tech support specializing in disks + dead servers I probably went through 30-50 scenarios).

2. Yes you can remount the volume. For Windows at least you can't run your OS on a software raid 5 array so if you blow your OS, it doesn't really matter about the array.

Having said all that you should still go for Hardware Raid 5. The caching and low cpu overhead make it perform much better. For Raid 0 or 1, software works just fine. I would lean towards hardware for raid 0, but software for raid 1.

Also, this is a completely stupid statement with no factual backing:

windows has crappy S/W Raid, as opposed to Linux, where S/W raid is pretty good.

Please never confuse Raid 1 or 5 with backups. Raid is designed to protect your uptime and NOT your data. It is merely a way to throw a drive without the server going down. It should never be used as a substitute for good backups.

 

[imported_goku]

How would you reinitialize a Raid 5 array if windows goes bad and you reinstall? Doesn't windows have a special signature? How do you add more drives to a raid 5 array for windows?

 

[Nothinman]

1. Hardware raid doesn't fail as gracefully as software. I've seen numerous times where a failed drive will wreck the parity information across all drives in an array leaving you with 3 or more useless drives instead of just one. When a drive fails in software raid it either fails gracefully or the OS goes down at the same time preventing junk data from being written to the other drives. It sounds odd but once you've seen enough failures you'll spot the trend as well (When doing tech support specializing in disks + dead servers I probably went through 30-50 scenarios).

I would guess that you either had really crappy controllers or drives that didn't properly report errors. Hardware RAID has a much better chance of working properly, provided you have drivers that do their job well. We have hundreds of servers and I've never seen a dying drive affect the rest of the array.

2. Yes you can remount the volume. For Windows at least you can't run your OS on a software raid 5 array so if you blow your OS, it doesn't really matter about the array.

With Windows you have to through that importing bs, but yes it should work.

Also, this is a completely stupid statement with no factual backing:

windows has crappy S/W Raid, as opposed to Linux, where S/W raid is pretty good.

Please never confuse Raid 1 or 5 with backups. Raid is designed to protect your uptime and NOT your data. It is merely a way to throw a drive without the server going down. It should never be used as a substitute for good backups.

[/quote]

I'm confused as to where you saw someone mention using RAID for backup purposes. I read the posts a few times, but maybe I'm just not seeing it.

And the factual backing for the superiority of Linux SW RAID is there if you know Linux software RAID. Just the fact that you can run RAID levels 0, 1, 5, 6 or plain linear mode in any combination puts it ahead of Windows. Then with the device mapper stuff you can incorporate encryption, multipathing and snapshotting. And there's also a full blown LVM setup available with online resizing and other crap that I can't think of right now.

 

[imported_goku]

bump

 

[nweaver]

Originally posted by: Smilin


Also, this is a completely stupid statement with no factual backing:

windows has crappy S/W Raid, as opposed to Linux, where S/W raid is pretty good.

Please never confuse Raid 1 or 5 with backups. Raid is designed to protect your uptime and NOT your data. It is merely a way to throw a drive without the server going down. It should never be used as a substitute for good backups.

no factual backing...I've used both. Linux has MANY more options and is much better and FASTER.

Also, you should look at who posts before you say that. I am someone who ALWAYS points out that RAID 1 IS NOT A BACKUP! I am probably one of very few people who has a tape drive for backups on my main system.

 

[imported_goku]

bump

 

[Smilin]

hehe I knew it would stir up the hornets nest when I came in here with the exact opposite answer to what everyone had already posted.

First, everyone seems to be taking offense that I mentioned raid is not for backups. If you knew this already good for you. I wasn't implying that YOU in particular didn't know. I've seen way to many people on AT griping about lost data when an array failed. Call it a public service announcement or something.

As for Linux & Windows (boy this will get religious real quick!)...
Windows does raid 0,1,5,10. It doesn't do 6 which generally performs poor compared to 5 and has more space overhead. It does linear mode (if you mean JBOD I think). You can do any combination, can include hardware raid (software mirror of hardware stripes) all that yada yada. Encryption is available in Windows completely separate from Raid and so are snapshots. You can expand JBODs and you can expand the size of volumes on that reside on hardware raid controllers. I'm not real sure what other fancy features you would really want. With the CPU overhead, non-battery backed up cache and all that you should really be using hardware for raid 5. I certainly don't think Windows has "Crappy S/W Raid".

If you have not seen a single failing drive blow a whole hardware array you've been lucky. I know lots of people here manage hundreds of servers but I also supported hundreds of admins in similar situations (I guess that puts my sampling of servers in the multiple thousands). I rarely got a chance to speak with people when a problem didn't happen (why would they call?) but I have seen MANY times where parity information simply collapsed on an array full of good drives. I've also seen MANY cases where a single drive fails and suddenly you have a corrupted volume. I've never seen this happen with software raid. It either works as advertised or the problem snuffs itself out in the form of a dead OS before data corruption can occur.

So I guess that's my story and I'm sticking to it. I don't find hardware raid to be any more reliable than software raid. It can't make a failing drive not fail and the only real thing it has going for it is battery backed up cache (which might make the difference between a track making it to disk or not, but won't save the whole array).

The "importing bs" that nothingman mentioned is simply a right click/import. It just makes an adjustment to the LDM database header on the drive to make it match the new OS. Nothing to do with the data in the array. The only time I've seen it not work is when some third party crap was putting it's fingers in the pie.

 

[Smilin]

Originally posted by: goku
How would you reinitialize a Raid 5 array if windows goes bad and you reinstall? Doesn't windows have a special signature? How do you add more drives to a raid 5 array for windows?

Disk manager, right click, import.

The LDM database on a dynamic disk is identical on each drive in the system. If you put the drives in a "new" system dynamic disks already on the system and newly added dynamic disks from and "old" system won't be included in each others database. The import process just changes the system ownership signature on the imported disks then ensures that all LDM databases on the system are identical again. Often times the only existing disk on a system is a basic disk which doesn't have an LDM database. No real conflict in that case.

No way I know of to add new drives to a sw raid 5 array. Use a hardware array in that case then simply expand the size of the volume with the diskpart command.

 

[randalee]

Originally posted by: Nothinman
We have hundreds of servers and I've never seen a dying drive affect the rest of the array.

Same experience here. We use both HP and Dell servers, and I've never had that type of problem. And we're talking hundreds I work with as well.

 

[Brazen]

In Windows can you get the system partition onto a software RAID array?

 

[Rilex]

Yes.

 

[Brazen]

Originally posted by: Rilex
Yes.

Windows XP? or just the server? How do you do it? You have to upgrade it to a dynamic disk right? but I didn't think it would allow you to upgrade the disk with the system partition.

 

[Rilex]

XP should let you create a RAID1 volume, but I've never done it. I converted the system/boot partition to dynamic disks then added a second disk to create a RAID1 set.

It also adds a nifty entry in boot.ini so you can boot to the second disk if the primary fails.

 

[TGS]

I've only worked with a few hundred boxes at a time, but I've never had a failure on a hardware array from a single disk. I've never seen it on external DAS arrays, on SAN arrays, or on NAS arrays either. I would be interested in what kind of adapter was the root culprit, and if there was some hardware problems with it.

Linux seems to offer better flexibility in the options you get for software RAID. With a combination in hardware options with software tuning over it, allows the end SA to do some very granular configuration that isn't available in the Windows environment, yet.

Hardware is more than just battery backed cache, you are missing the entire point of running parity based RAID on hardware. The XOR processor. For particular hardware, housing a DAS array, if you are pounding the machine with system calls and passing massive amount of IO the machine will choke trying to process both. You add the hardware based solution, and offload the parity calculations to the XOR processor you can actually have a functioning box.

As far as I know the logical disk manager for windows is a Veritas joint venture product. Which means that a third party is always involved with LDM operations.

 

[Dravic]

Anyone using ANY form of RAID as a backup solution will be eventually without their data.


RAID is for hardware redundancy, NOT backups... get yourself a real backup solution. If you delete/destroy the data, its deleted destroyed on all the drives. Meaning, raid wont stop YOU from overwritting or deleting anything.



my .02c hate seeing raids used as data security..

 

[nweaver]

did you read the thread? It's mentioned several times that raid is for uptime/redundancy in H/W, no one here claims it's for a backup, as most of us realize that it's a rediculous prospect.

 

[Brazen]

Originally posted by: Rilex
XP should let you create a RAID1 volume, but I've never done it. I converted the system/boot partition to dynamic disks then added a second disk to create a RAID1 set.

It also adds a nifty entry in boot.ini so you can boot to the second disk if the primary fails.

Ok, I should have just tried it before (I think maybe I tried it on Windows 2000 and it wouldn't upgrade the system partition to dynamic disk). I tried it on my XP machine and it looks like it will let me create a mirrored drive, but what I'd really like is RAID 0, and it looks like it won't let me do that. Guess I'll just have to wait until I upgrade to a mobo with RAID 0.

Does anyone know if Windows XP's software RAID 1 is smart enough to split the reads between the drives, for added performance?

 

[nweaver]

it won't split, as that's not what raid1 is about.

Raid0 is very overrated. I only run it so I have double space in a single "partition" on my windows box. If I could get linux drivers for my scanner, I wouldn't run raid0, I would run sw raid 1 on 2 partions for some stuff, and then mount the other partitions as needed elsewhere.

 

[Brazen]

Originally posted by: nweaver
it won't split, as that's not what raid1 is about.

Raid0 is very overrated. I only run it so I have double space in a single "partition" on my windows box. If I could get linux drivers for my scanner, I wouldn't run raid0, I would run sw raid 1 on 2 partions for some stuff, and then mount the other partitions as needed elsewhere.

I'm not sure you understand what I am asking. Raid 1 is about having two exactly identical partitions. When writing data, the data must be written to both drives; but when reading data, most, if not all, hardware raid cards will read half the data from one drive and half the data from the other drive.

My question is if Windows XP's software RAID 1 is smart enough to read half the data from one drive and half the data from the other drive.

edited: because I messed up Raid 1 with Raid 0.