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Can we add 3rd hard disk in Raid1

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October 28, 2012 2:56:44 PM

Hello, we are goingto instal a server. I understand that the OS should be in Raaid 1 and dta can be in raid 5. Is there any issue if I put OS in RAID 5 ?

a b G Storage
October 28, 2012 3:20:35 PM

No there isn't an issue

. Some of the systems(server) I have built were a raid 5 only system. i created a large raid 5 and created an OS partition, and a data partition within the raid 5.

Some people like to separate the OS and DATA and put them on separate physical drives.

a c 81 G Storage
October 28, 2012 3:21:15 PM

Yes! :)  Well, it depends. The typical server setup with a hardware raid controller has two small disks in raid1 for the os and at least three disks in raid5 for data. The raid1 is faster, especially when one disk fails. And you can make a block based backup, opposed to a file based. The raid5 is always slower, especially when a disk fails an has to be rebuild. With the os on it, the server will be unusable until the disk is rebuild and that can take many hours. Os and data on the same raid is always a bad idea, because you get a very high I/O load on one channel. Put the os on a single ssd instead. They are unlikely to fail as fast as disks do, because they have no moving parts and you can add a second one for raid1 later.
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a c 81 G Storage
October 28, 2012 3:27:11 PM

ss202sl said:
No there isn't an issue

. Some of the systems(server) I have built were a raid 5 only system. i created a large raid 5 and created an OS partition, and a data partition within the raid 5.

Some people like to separate the OS and DATA and put them on separate physical drives.


Two people, three opinions. That's the main fun on this forum. :) 
a b G Storage
October 28, 2012 3:43:05 PM

noidea_77 said:
Yes! :)  Well, it depends. The typical server setup with a hardware raid controller has two small disks in raid1 for the os and at least three disks in raid5 for data. The raid1 is faster, especially when one disk fails. And you can make a block based backup, opposed to a file based. The raid5 is always slower, especially when a disk fails an has to be rebuild. With the os on it, the server will be unusable until the disk is rebuild and that can take many hours. Os and data on the same raid is always a bad idea, because you get a very high I/O load on one channel. Put the os on a single ssd instead. They are unlikely to fail as fast as disks do, because they have no moving parts and you can add a second one for raid1 later.



Raid 5 is faster than raid 1. Raid 5 has more disks, raid 1 is just 2 disks mirrored.
a b G Storage
October 30, 2012 9:47:52 PM

pathak said:
Hello, we are goingto instal a server. I understand that the OS should be in Raaid 1 and dta can be in raid 5. Is there any issue if I put OS in RAID 5 ?


It's a confuse.
The title stated: Can we Can we add 3rd hard disk in Raid1 - but the thread is OS in RAID5?!!.

Well I'll cover both. lol
1) Can we add 3rd hard disk in Raid1
The answer is YES.
http://www.datoptic.com/three-bay-mirror-raid-enclosure...

We did use this in a server that server about 50x stations. We use four 2TB HDD.
Three connect to server, the fourth HDD is off site back up.

Everyday we switch out the HDD from the three drive Mirror raid for off-site total back up (OS+DATA).
The nice things about this is:
- There are dual drives redundant and the OS never goes to critical condition. Even in the rebuilt mode, if the primary drive failed during rebuilt, there is secondary drive ready to take over. Like RAID6 redundant but in RAID1. This ensure dual drives OS presented all the time

- Let say for what ever reason the server is damaged. User can rebuilt the system with the remote back up HDD with very little time, because OS and DATA all in ONE HDD. Just drop this backup HDD in a new system and boot.

2) Is there any issue if I put OS in RAID 5
There is no issue to have OS in RAID5, but there are things you need to aware.
a_ Boot-able MBR volume can not be greater than 2TB
b_ Space beyond 2TB of RAID5, user may not able to use/access.
c_ Built RAID5 takes hrs
d_ It is fast, but you data is limited by Ethernet Gb, so it's not much important.
!