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I have a general purpose server which is running out of disk space. It currently has a RAID1 of two 2TB disks (WD RE4). So I'm going to buy two 4TB disks. I am considering the following options:

  • Make a RAID0 of the 2TB disks, then a RAID5 of the three 4TB volumes (two physical + 1 logical), for a total of 8TB

  • Leave the RAID1 array as it is, make another RAID1 of the 4TB disks, then a RAID0 of the two logical volumes (2TB + 4TB) for a total of 6TB (mdadm does not waste space with RAID0s made from different sizes);

  • Leave the RAID1 array as it is, make another RAID1 of the 4TB disks, then use LVM to combine everything into a 6TB volume group.

Is there a better solution I haven't thought of? Are there any obvious drawbacks or errors in the above options?


Edit: the server has many roles (web, ftp, nfs, database, gateway, etc), probably the heaviest I/O is made by the recordings of the security cameras. There are about 10 clients, divided among desktops, laptops and embedded devices. There is a backup NAS, but backups are not made exactly daily...

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You left out 'leave the RAID1 array as it is, make another RAID1 of the new 4TB disks', mount the new array somewhere, keeping two separate arrays. Depending on your usage of this general purpose server that can be an advantage or a disadvantage. – Hennes Dec 1 '12 at 23:26
Correct. I'd up-vote but I cannot yet... However I wouldn't really know how to split the data between the arrays, as there isn't really a logical distinction. – Alberto Dec 1 '12 at 23:49
up vote 0 down vote accepted

It might help if you were to elaborate more, like types of apps you host, what OS you are hosting, how many clients, etc.

There are advantages and disadvantages to every RAID scenario, hence the plethora of scenarios and the multiple RAID choices. You really have to evaluate your personal needs and just make the best choice you can.

I wouldn't recommend RAID 0 though for any server, unless you don't care if the array crashes (temp files or you have awesome backups and no RTO restraints).

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I agree that a single RAID0 is definitely not advisable on a server, but do you think it is also as bad if it is somewhat protected (by a RAID5 or RAID1)? – Alberto Dec 1 '12 at 23:38
It's up to you really. I wouldn't put any critical data or apps on the RAID 0 but you could use it for something that doesn't need to be concerned with failure. – TheCleaner Dec 1 '12 at 23:54

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