NAS Raid Guidance Please

[Syd]

Morning to you all

Prompted by reading a review of Nas boxes this month in Custom PC, I have come to realise that it really is about time that I buy myself some sort of network available storage and backup system.
So I am thinking one of the NAS boxes with a pair of 1.5TB drives in Raid Mirror will give me both those functions............

Only thing is I have read before that raid mirror DOES NOT provide a foolproof backup function - but in the review It states that it does, hence my confusion!!

I basically have about 150GB of photos 500GB of music and 50GB of archived nonsense that I would like to protect. So if I did what I was thinking would I be protecting myself and allowing access printer, memory stick to both machines as an extra benefit??

Thanks
Syd

[Salazaar]

Mirroring provides a backup in case one drive fails, in which case you replace the drive and rebuild the array.

However, if your NAS box fails you have no external backup and you either lose the data or hope that you can rebuild or extract it somehow.

And IMHO, Custom PC has been going down the tube for some time now.

[kingpotnoodle]

RAID 0 = Striping, result is higher performance on read and write but NO redundancy, double the risk of data loss. Use only where the data is transient/temporary and performance matters most.

RAID 1 = Mirror, redundant because if one fails you have another copy. Performance is usually similar to a single drive although some fancy controllers can increase read speed by using both drives. Rebuild is a simple copy, can be time consuming and data is vulnerable during the process. Not the most economical as usable capacity is 1/n but only requires 2 drives for redundancy.

RAID 5 = Striping with distributed parity blocks. Read speed increases but writes are generally worse, a drive failure will reduce performance. Redundant because data can be reconstructed using the parity blocks, time consuming and processor intensive to calculate. Data is vulnerable during the rebuild. Economical as usable capacity is 1-1/n but requires minimum 3 drives.

RAID 6 = Striping with double parity blocks. Same as RAID 5 but using double parity and can tolerate 2 drive failures before data is lost. Data is not vulnerable during the rebuild of first failed disc. Not so economical as usable capacity is 1-2/n and requires minimum 4 drives, economy increases the larger the array though.

RAID 10 = A stripe of mirrors. Fast like a RAID 0, redundant like a RAID 1. Often used in high transaction environments like databases, common in the datacentre. Can tolerate a drive failure in each mirror set.

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RAID 6 is the safest, but I'd recommend 1 or 5 for home use. It's unlikely in a small array 2 drives will fail at the same time.

Don't trust a RAID to protect your data though, if the NAS fails or is destroyed by fire/theft/electric surge etc then you'll lose the data too. Offsite backup should be used for anything that you really cannot afford to lose.

RAID should be seen as a way to reduce the hassle of recovery from drive failure - i.e. you don't have to go to the backup and restore it.

[babaracus]

Only thing is I have read before that raid mirror DOES NOT provide a foolproof backup function - but in the review It states that it does, hence my confusion!!

Raid 1 will keep an exact duplicate of your data on (in this case) two drives. If one drive fails you still have a copy of the data on the other disk.

However if your data becomes corrupted - some of your photos refuse to open etc - the corruption will be mirrored on both drives.

Remember that raid is not a backup

[Syd]

Thanks for the responses

However - now i'm still not sure what to do !!

Could I set up a 2 disc nas box to have 1 drive as the data drive and the other to backup the data drive, ie not RAID ? And would that be a safer solution ?

[Salazaar]

Could I set up a 2 disc nas box to have 1 drive as the data drive and the other to backup the data drive, ie not RAID ? And would that be a safer solution ?

That's essentially what a mirrored raid array is. But it won't protect your data if the NAS hardware failed or was damaged in some way.

To protect against that you'd need a full other set of hardware, preferably in an entirely different location, mirroring everything on your raid array.

[abaxas]

Raid 1 will keep an exact duplicate of your data on (in this case) two drives. If one drive fails you still have a copy of the data on the other disk.

However if your data becomes corrupted - some of your photos refuse to open etc - the corruption will be mirrored on both drives.

Remember that raid is not a backup

Exactly... just to remind people..

raid is not a backup


The 'R' in raid is redundancy. Ie to keep service on failure, not backup.

[watercooled]

Just in case you missed it RAID isn't about data integrity but availability and sometimes performance. Most home users however simply don't need that, despite most people accepting RAID as the norm for file servers/NAS boxes it's simply not necessary most of the time - JBOD or single disks is often the best choice for home users. Also note that rebuilding an array can be painfully slow, especially on the embedded hardware present in NAS boxes, usually taking much more time than restoring a backup. If the NAS itself is the backup then you could leave it at that, otherwise you'd be best backing up the NAS to either another NAS or depending on how much data is added to the NAS on a regular basis you could use USB HDDs to mirror the contents using rsync or something but that would depend on what's on it, if you need past archives etc.
SNB has an interesting article about using RAID on NAS boxes: http://www.smallnetbuilder.com/nas/n...s-dont-do-raid
This post is about WHS rather than NAS boxes but is still applies here and is really worth reading before you choose RAID over a backup: http://www.fearthecowboy.com/post/Wi...r-vs-RAID.aspx
Also I agree about CustomPC, I bought this months article and lots of the articles seem very unprofessional and I noticed a few mistakes like this, they also seem to assume everyone overclocks the pants of their system and are very biased towards Intel. They also didn't bother including another good NAS choice in the alternatives bit - using a Linux distro with Samba, what I'm doing which cost less than most of the decent NASes in that review and beats even the fastest NAS on test at transfer speed (I get 70-90MB/s).

[peterb]

Hmm - seems my mantra "RAID is not a backup" is being widely adopted - which can only be a good thing!

As others have said, RAID1 is about data resiliance and server up time as much as anything. With two drives, if one fails the other keeps on going until the faulty drive is replaced.

However there is still a single point of failure - the disk subsystem itself.

So you do need to keep a backup. One solution is an external hard drive the same size as the RAID array and backup to that - when you have backed up disconnebvt the drive and put it away in a safe place where it won't get dropped. And for speed you may want to look at an eSATA interface on the caddy.

However remeber that as a mechanical device - hard disks WILL fail - the only unknown is when.

The other (expensive) option is a tape drive, but then tyou are looking at SAS/SCSI controller and a drive as well, and although the cost per GB of storage is riduculously low, the initial investment is pretty high. (As I type I'm backing up a 250Gb partition onto an Ultrium 2 tape - tape cost £20) and so far it has taken 3 hours. That said I copied the same data from a USB caddy and that took over 5)

[Syd]

This is the scary thing - CDR/BDR/HD all have a life and will fail at some point. I'm thinking that the only really important and irreplacable data is my photos, totalling about 150GB at present, so maybe a NAS to put my itunes library onto and phtos and then that will give me the ability to share and view over the network and then an external HD to back up onto. At that rate is there any advantage to running Raid Mirror ?

[watercooled]

IMO you're just wasting the space of the second HDD, stick it in a caddy and use it to back up instead.

[Syd]

IMO you're just wasting the space of the second HDD, stick it in a caddy and use it to back up instead.

I'm probably missing somthing obvious here, but could I not run both drives as single vlumes in the nas box - using one to back up the other but not in raid ? hence saving another box and another caddy ?

[watercooled]

Ideally a backup should be separate from the main HDD for a number of reasons including protecting it from a failing power supply, power surges, physical damage, etc otherwise you're only protecting against drive failure in which case you might as well use RAID.