I am trying to decide weather I should get RAID 1 in our new servers or not. I mean, if you have a good tape backup system in place or a reliable type of backup, is RAID 1 just in vain. I mean I would be using a quality Dell Server. What are the chances of a Hard Drive failure and even if one did happen, just replace the hard drive, and your going again. So is RAID 1 really worth the extra money involved?

If you server fits 3 hard drives, why not do a RAID 5? :cool:

I still can't graspe the concept of what RAID 5 really is. It's not disk mirroring so what is it?

raid 5 is disk striping with parity.

one of the 3 disks is used for the parity bit if one of the drives fails


take the following example

Parity

0 0 = 1
1 1 = 1
0 1 = 0

Disk 1 Data = 0
Disk 2 Data = 1
Disk 3 Data = 0

Lets Say Disk 2 Goes Down, take the data from disk 1 and 3 and what do you get using the parity check?

the data from the lost disk !!


if im wrong then someone correct me !! ive typed it exceptionally fast !

As a side note, RAID should be used for HD failure protection and not for HD backup. I've seen some people think that disk mirroring will protect them if a hacker hits their site, or if someone deletes something by accident and this is not the case.

BTW, you are right about how Raid 5 works.

Originally posted by MikeA
As a side note, RAID should be used for HD failure protection and not for HD backup. I've seen some people think that disk mirroring will protect them if a hacker hits their site, or if someone deletes something by accident and this is not the case.

I go even further, I have seen cases where the first HD got currupt due to a loop in the system, and mirror itself so well, it corrupted the second as well :eek:

I knew all that. What I am asking is if you have proper backup in place is RAID 1 really neccessary? Also, I know this will sound hard to believe and make me out to be an idiot but I still don't understand RAID 5 :rolleyes:

raid 5 is a "simpler" way of having a swapable drive incase of failure. Also, it helps recovery when a disk fails due to the math it uses. the Parity drive will recreate the failed drive.

But the great thing about it is... higher read spead passing into the computer.

I think ( correct me if I'm wrong) that raid 1 just mirrors but does not become the active drive of access unless of hard drive failure. while raid 5 lets some of the drive become accessable, you have more heads reading data to fill up the pipe faster.

-Sqposter / Michael

RAID as a technology is to protect against downtime as a result of a hard disk failure (except for RAID 0 but lets not complicate things). It does not take the place of a tape drive as it cannot protect from natural disasters (fire, flood etc) and if the data on a disk becomes corrupt you will still need to restore from a backup.

In RAID 1 the data from disk 1 is mirrored to disk 2 - if disk 1 fails the server continues with no downtime with disk 2 as the main disk. You can then hot swap the failed disk (if the server supports it which the Dells do) and it will then rebuild across the disks. Performance on RAID 1 is no better or worse than a single disk.

RAID 5 is slightly different in that it has a minimum of 3 disks and you lose one to redundancy (N-1). It is stiping with parity so it should be quicker for reads than RAID 1 but not a quick for writes as it has to calculate the parity across the drives.

The way XStrike explains it below is VERY close but in actual fact the parity is distributed across all the disks - if you use RAID 3 or 4 then it is all stored on one disk but the principle of how XStrike explains it is spot on.

The brand of server and disk makes no real difference - disks account for 55% of server downtime from hardware failure followed by PSU, fans, NICs, memory errors etc. The reason the disk is so problematic is that it uses moving parts and generates heat which is a recipe for disaster. In my experience it is not unusual to experience at least one disk failure in the life of a machine and sometimes you can be damed unlucky and suffer more than that.

My advice would be to use RAID and a good tape backup and that way you are pretty well protected no matter what happens.

Sorry for going on but like I said, it it the first question I have ever been able to answer on here!!!

Mondeo

Originally posted by netsolutions
I knew all that. What I am asking is if you have proper backup in place is RAID 1 really neccessary? Also, I know this will sound hard to believe and make me out to be an idiot but I still don't understand RAID 5 :rolleyes:
Nobody yet has answered my main question. And I still don't under stand RAID 5. What the heck is striping with parity or whatever. Can anyone explain this without using other RAID terms or no?

Basically, RAID5 gives you the best of both worlds. It is fast, and mirrors your data, as opposed to one or the other in different configurations.

10 replies and still no one has answered my main question ;)

go to http://www.acnc.com/04_01_05.html - that explains RAID 5 in the best terms I have ever seen.

As for answering your main question I believe they have all been answered:

I am trying to decide weather I should get RAID 1 in our new If you have a good tape backup system in place or a reliable type of backup, is RAID 1 just in vain - NO

What are the chances of a Hard Drive failure - PRETTY HIGH, 55% OF HARDWARE FAILURES ARE HDD RELATED

And even if one did happen, just replace the hard drive, and your going again - BUT YOU HAVE TO RESTORE THE DATA AND YOU HAVE DOWNTIME WHILE RESTORING THE DATA ETC AS WELL AS THE DELAY IN BEING INFORMED THAT A DISK HAS FAILED

So is RAID 1 really worth the extra money involved - IF THE SERVERS ARE MISSION CRITICAL, YES. IF THEY ARE NOT MISSION CRITICAL, NO.

Hope it helps

Mondeo

So what do you consider mission critical?

I think it is all about money.
If you have extra cash, then go for it.

I never had a hard drive failure before, so I think your server will be obsoleted before your hard drive go dead.

You should take a poll to see how many people have had hard drive failure before. I believe the chance is very low.

:cool:

Originally posted by netsolutions
So what do you consider mission critical?

Anything which will cost you money, stop you doing business or damage your reputation as a company if it goes down. You need to make the decision based on what you are proposing using it for.

If you offer, for example, a 99.5% uptime guarantee on a web server then you can only have a maximum of 4 hours downtime in one month. If you get a disk failure it could well be down for longer than that and then it starts costing you money and potentially customers. Think how long it would take you to replace the disk, reimage the box and then restore the content - it could take that long easy and that is asuming you found out about the failure the moment it happened (which is easy to do using server monitoring packages such as Dell Openmanage or Compaq Insight Manager).

Even if it doesnt take 4 hours to fix the disk customers will be pissed if their server is down for 4 hours and you could lose business.

Regarding Asias comments about how many people have disk failures, I work in the hardware industry and I would estimate that on a server running 24 x 7 you would get at least one disk failure in a three year period and maybe more.

Jason

I think I know what I have to do now. RAID 1 here I come :)

Originally posted by netsolutions
I think I know what I have to do now. RAID 1 here I come :)

netsolution,

Good decision! Good Luck! :stickout

Originally posted by netsolutions
I think I know what I have to do now. RAID 1 here I come :)

if you can afford it go raid 5 instead. slight better read speed and the cost factor is minimal. plus you get a little more hard drive space( i think).

I work in the hardware industry and I would estimate that on a server running 24 x 7 you would get at least one disk failure in a three year period and maybe more.

That's interesting. Since almost all good SCSI hard drives have a 5 year warranty, that would mean that almost all disks used in servers would be replaced within warranty. I can't believe if they fail this often that they would actually give you a 5 year warranty - 2 for the price of 1 :eek:

That's a very good point. I never thought of it like that.

Originally posted by scott2


That's interesting. Since almost all good SCSI hard drives have a 5 year warranty, that would mean that almost all disks used in servers would be replaced within warranty. I can't believe if they fail this often that they would actually give you a 5 year warranty - 2 for the price of 1 :eek:

fair point but like I said I am speaking from personal experience. If anyone disagrees then please say so - I guess you could be exceptionally lucky and never get a disk failure and you could be very unlucky and get lots in the three year period (which is the typical warranty period offered by server vendors).

Its all about Murphys Law, I guess. You dont get it and you will have disks fail, get it and nothing will ever fail and in three years you will be asking yourself why you wasted the extra money to deploy RAID.