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I am setting up a NAS box, but money is a bit short right now. I am planning on getting the box up and running with a boot drive, then 3 for a RAID 5 config with some lower end drives.

I was reading online about a bunch of the complications that can arise from people not setting it up right, and couldn't get a feeling of exactly how hard/feasible it would be.


  1. Is it possible to upgrade (replace a drive with a bigger/faster one) and/or add drives (without wiping, and rebuilding)?
  2. How risky is it to do this with data that isn't backed up (because of sheer volume)?
  3. Any tips/advice I should follow to set up a best case in the future to allow upgrades?

Note, I'm really between a RAID 5, and a RAID 01. Would this be easier to upgrade a RAID 01?

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What is your use case for this NAS? – EEAA May 28 '11 at 5:08
up vote 6 down vote accepted

Instead of a single boot disk and 3 disks in RAID 5, consider 4 disks in RAID 10. This is both faster and safer. You do not want your NAS to go down if the single boot disk fails. Additionally, RAID 5 has poor write performance and does not rebuild reliably on large, terabyte-denominated volumes, especially when you are using inexpensive drives.


  1. Replacing a disk with a larger one: Not with a standard RAID controller. Some vendors (e.g. Drobo) have proprietary RAID implementations that support adding disks of dissimilar sizes, etc., but traditional RAID remains far more dependable. If you want to play with something dynamic and innovative, I would suggest ZFS. Added in response to TomTom's observation that only half of question #1 had been answered: Expanding an array by adding disks of the same size as existing array members is supported by many enterprise RAID controllers. Larger disks will be treated as though they are no larger than existing disks. This may be unsupported by low-end/integrated RAID devices. Check the documentation for your specific controller.

  2. No. RAID is never an excuse for failing to have a backup and a DR plan. Having "too much data" is also not an excuse for failing to back up; however, it may be an opportunity to assess whether any significant portion of your data can be classified as genuinely unimportant.

  3. With consumer grade 2TB SATA drives costing only $80 each in 2011, and enterprise-grade 2TB SAS drives costing only $240, you can add 4TB of usable RAID 10 capacity for $320 (consumer-grade) or $960 (enterprise-grade) if you have sufficient bays and connectors. That's a very cheap incremental upgrade path.

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The problem with the backups is the fact that this is meant as the main storage hub (where I will backup my computers to), where would I put a backup of this? – Ben May 28 '11 at 7:37
"Noit with a standard raid controller"? Joking? Seriously? You use 10 year old stuff? All - areca, adaptec, 3ware - suppot capacity expandion online these days. For quite some time. – TomTom May 28 '11 at 7:40
Increasing capacity by adding additional drives of the same size is a separate question from "can i replace a drive with a bigger/faster one." It appears that I erred in answering only one of the two questions. – Skyhawk Jun 2 '11 at 16:37
Be very cautious about using workstation grade HD's in a RAID array - they aren't built for the vibration problems you encounter by putting a lot of drives next to each other. You will have a much higher failure rate, and your overall performance will suffer. (This is only to amend the data in comment 3 to encourage purchasing slightly more expensive, but correctly designed drives for the purpose you have). – Neil Neely Jun 2 '11 at 16:49
@mazzzzz: Where to back up? That's up to you. If you are planning to store backups and live data on this array, be sure to create a separate "backup" share or folder so that you can exclude it from your backups of the live data. In poorly managed disk-to-disk backup scenarios, people can inadvertently make backups of backups of backups and then wonder where all their space went. – Skyhawk Jun 2 '11 at 16:50

Re 1: depends. On technology used, which you say nothing about. I use Adaptec raid controllers, and thy do that, without pulling the raid.

Re 2: depends how much you value your data. I copy all data to another server or two with large slow drives.

Re 3: Except investing oney into a decent raid controller and making sure you have the hardware layout in place for that? For example, what is expansion for you? I run a 24 slow server for that reason (to allow expansion), rack units. Now i start filling up the last 8... the next server will be a 4 rack unit 72 bay machine allowing me to put in 72 discs. But then, this costs (just th case) around 3000 USD, so "cheap" and "expansion" are very relative terms, you know.

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Regarding question 1:

Yes, it is feasible to expand a RAID 5 by either adding more disks or by replacing existing disks with larger disks. "The maximum number of drives in a RAID 5 redundancy group is theoretically unlimited." [1]. Ask yourself first, however, whether your filesystem will support this operation. Adding larger disks needs to be done across the entire RAID before you will be able to recognize the benefit.

Regarding question 2:

I would characterize a RAID reconstruction as inherently risky. I do it all the time but I never do it without careful thought and a bit of nervousness.

Regarding question 3:

Look at LVM. Also, consider using an external JBOD (just a bunch of disks) instead of trying to cram all the drives into a standard chassis. Disks are relatively cheap. Go SATA. You can get 3TB SATA drives for $150. Buy the best RAID card you can afford. I've had good luck with LSI and Adaptec.

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Is it possible to upgrade (replace a drive with a bigger/faster one) 
and/or add drives (without wiping, and  rebuilding)?

That depends on the precise bit of kit you buy. It's a device specific issue.

How risky is it to do this with data that isn't backed up (because of
sheer volume)?

Lets be clear about something - RAID is not a backup, period. Anyone who stores data on a drive system without backing it up is a fool. That's without even considering the potential for issues with changing drives and expanding the array. If you change the properties of a RAID array without backing up any important data you store on it first then you must be mad.

Any tips/advice I should follow to set up a best case in the future to
allow upgrades?
  1. Carefully research the product you wish to buy and make sure it supports this functionality.
  2. Plan for backups anyway, never mind during array expansion.
  3. Be wary of special offers on "End of Life" NAS systems, which may not support newer, larger hard disks, thus limiting your expansion potential.
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