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DAS, NAS, RAID 5...What do I need?

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July 11, 2009 2:37:09 PM

My goal is to have redundant (this being the most import) storage for general data and also a place to store my user(s) accounts for my Open Directory (similar to Active Directory), something in the 2-5TB range. One thing I do NOT want is a system that requires a PCI card. This will be used on a small home, all Mac, network; about 5 - 8 systems.

I was first looking into a DAS RAID 5 box with firewire 800 (Drobo) but am thinking about a NAS RAID 5 box (ReadyNAS NV+). I wanted to hear what you guys thought would be a good solution. Obviously, cheaper is always better but am thinking around the mid $400 range with no drives.

Thanks for you thoughts.

More about : das nas raid

a c 127 G Storage
July 11, 2009 5:22:27 PM

For that money you can build a computer dedicated as NAS, with the ability to expand in the future, higher performance and all the flexibity you want. You can put FreeNAS on it and get a NAS running in 10 minutes, or you can setup an advanced config.

First, is redundancy all you need? Even with RAID5 i lost data in the past, and not because of drive failure but filesystem corruption. I realized i needed a backup even though i thought i was safe with RAID5. Nowadays, ZFS can also help protect against corruption, by checksumming your files and using redundant data to fix the corruption. But if you go a traditional route i would encourange to build two of the boxes, so one can act as backup, but does not need to be powered on most of the time.
July 11, 2009 5:43:00 PM

sub mesa said:
For that money you can build a computer dedicated as NAS, with the ability to expand in the future, higher performance and all the flexibity you want. You can put FreeNAS on it and get a NAS running in 10 minutes, or you can setup an advanced config.

First, is redundancy all you need? Even with RAID5 i lost data in the past, and not because of drive failure but filesystem corruption. I realized i needed a backup even though i thought i was safe with RAID5. Nowadays, ZFS can also help protect against corruption, by checksumming your files and using redundant data to fix the corruption. But if you go a traditional route i would encourange to build two of the boxes, so one can act as backup, but does not need to be powered on most of the time.


Yes, Data loss is the biggest need, otherwise I would just setup a JBOD. The corruption subject is a good thing to bring up, as I hadnt thought about that. I will have to look into ZFS (I believe OSX Server supports this format). One question I have about ZFS is:
-I add a 2nd 500G drive for a total of 1TB (and my understanding it automatically adds this space to the current volume)
-I only have 250GB' of data
-One of the drives fail, again only using 1/4 of the 2 drives combined storage
Do I lose all data?

Now part 2
-I add a 2nd 500G drive for a total of 1TB
-I NOW have 750GB's of data
-One of the drives fail, do I lose all data (maybe just the data on the bad drive)?
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a b G Storage
July 11, 2009 6:54:38 PM

zfs is a file system like fat32 or mfts, all your questions depend on type of raid array you are using.

here is an overview of raid levels'
http://www.acnc.com/04_01_00.html
July 11, 2009 9:43:33 PM

Thanks for your comments. I am still looking to see what you guys/gals think I should get, DAS or NAS?
What box do you think I should get for that?

The Linux box might be an option, will have to look into how much of a PITA it really is. On that note, doesnt FreeNAS use a software RAID. What would be the advantage/disadvantage to a software or hardware RAID 5 setup

Thanks again
a b G Storage
July 12, 2009 6:07:27 AM

in software raid all the calculations are done by the cpu; where as in a hardware raid you use a expansion card that has it's own processor to handle raid calculations.

it is a matter of goals and preferences as to what system you want to use. You have to do some research and get an idea of what you want: Hardware/Software, Windows/Linux, What level raid,...

Once you have a system laid out people can help you fine tune it, right now it is to vague a question.
a c 127 G Storage
July 12, 2009 12:56:39 PM

If you go Linux/FreeNAS then you do not need a hardware controller ofcourse. And if you pick ZFS, ZFS has its own internal RAID engine (RAID0, RAID1, RAID5, RAID6).

You can even create a ZFS config with 2 disks in RAID0, then configure the directory /important to store two copies of each file, and if one disk fails you still can access the /important directory because a copy is kept on both disks; so essentially its a RAID1. But you can keep other directories on copies=1 so they would have no protection, but only important stuff has an additional copy.

Likewise, should one copy fail because of file corruption, ZFS will detect that and fix it by using the redundant data / file copies. This is a very important feature, and i couldn't imagine a filesystem without checksums. Just yesterday i had a corruption issue, on a Ext4 filesystem where i had to replace one binary data file, its md5 was different than on my other machines even though this is a read-only file. I'm guessing this is a bug in Ext4, but with ZFS i can at least watch the corruption:

  1. NAME STATE READ WRITE CKSUM
  2. flash ONLINE 0 0 0
  3. raidz1 ONLINE 0 0 0
  4. ad14a ONLINE 0 0 0
  5. ad4a ONLINE 0 0 0
  6. ad6a ONLINE 0 0 0
  7. ad10a ONLINE 0 0 0
  8. ad18a ONLINE 0 0 0
  9. ad12a ONLINE 0 0 0
  10. ad16a ONLINE 0 0 0
  11. ad8a ONLINE 0 0 0


The only drawback is that you cannot expand a RAID-Z (or RAID-5) volume in ZFS. Only RAID-0's are expandable. Ofcourse you can still use the copies=2 thing on some or all directories if you like.
July 16, 2009 7:12:03 PM

do you care about performance?
DAS= block level access
NAS=file level access
!