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ReadyNAS 104 Convert X-Raid to Flex Raid - will it expand space for data?
Hi,
Before I start, my NAS is a media server and im not really bothered about backup and data recovery on it as nothing on it is crutial that it is kept.
Having said that I have a lot of data on a 2TB drive (which is also spread across several other drives)
I bought the NAS to replace a kubuntu server running samba with seperate drive shares (currently a 14port usb set of smaller drives - speed is not essential). The idea was to eventually install 4 x 2tb disks to get 8tb in the NAS.
Knowing nothing about how RAID worked when I started, I set up and have running the NAS with about 1.6TB of data on a 2Tb disk. I have since installed another 2tb disk before realising to my horror that the volume didnt expand to 4 tb.
Well now I did some research on raid. A bit late I know! It is infact now mirrored, so the same contents are on both drives. and there is 4tb of disks but only 2tb avaliable.
I have done a lot of reading since but I am still not sure I understand fully.
With x-raid if I understand that the space will expand, when I add a 3rd 2tb disk, but what space does it expand to - which amount of TB? I understand that a 3rd disk will change it to raid-5
I also understand that in OS6 (which I have) that I can toggle between x-raid and Flex-Raid without loosing data, but will this convert the 2x2tb drives into a 4tb drive or will it make 2 x 2tb drives that need seperate mounts in windows? This is where i dont understand how it works and i feel rather inept at this point because everything i read talks about redundancy etc, which I understand but i cannot acertain from the information if the space will expand.
What I want is for 4x 2tb drives to be 8tb but accessed a 1 large volume - ie 1 drive. Striped or not striped, im not bothered, but i want to be able to expand to 8tb with 4x2tb drives. Again I dont really need speed as no more than 2 or 3 machines will access at once and then only intermittantly, and not much more than 3000kbit/s would be required.
Any help or clarification would be greatly appreciated.
6 Replies
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Adding another 2tb disk will expand your volume by 2tb and yes it will effectively be raid 5.
Toggling to flexraid will do nothing. The volume will stay as it is. You cannot change the raid level without destroying the volume.
I would advise against a single multi disk raid 0 volume as a single disk failure causes loss of the entire volume's data. Separate volumes on each disk is more sensible.
As you have an additional disk you could change to flex raid, add the disk and create a new single disk volume. Once the new volume is created, copy the existing data from the raid 1 volume onto the jbod volume, then destroy the raid 1 volume you have now, and use the 2 original disks to create 2 more jbod volumes. This will leave you with three 2 tb volumes, You can of course add a 4th.
Update your firmware before you start this.
- Hi, thanks for the reply.
So to clarify, 3x 2tb disks in x-raid becomes 4tb raid 5 with data recovery possible.
So what does 4x 2tb become - 6tb?
My next question will be if 4x 2tb x-raid become 6tb how is it possible to recover 6 tb of data from 3 drives if 1 fails, and worse still if 2 fail?
mickle026 wrote:
So to clarify, 3x 2tb disks in x-raid becomes 4tb raid 5 with data recovery possible.3x2 tb xraid is raid-5. If you change to flexraid it remains raid-5. There is protection from loss of a single disk.
mickle026 wrote:
So what does 4x 2tb become - 6tb?Yes.
mickle026 wrote:
My next question will be if 4x 2tb x-raid become 6tb how is it possible to recover 6 tb of data from 3 drives if 1 failsAre you asking how RAID-5 works?
If so -
Data is organized as "stripes" across the three drives. For each stripe, there are two data blocks (on different drives), and a parity block on the third drive.
The parity block is the logical xor of the two data blocks. You can think of this as the sum of the two data blocks (xor is analogous to addition in a Galois field - which is used in RAID-5 and RAID-6)..
So if D1 + D2 = P, then if one of the data blocks is missing, it can be reconstructed as
D1 = P - D2 or
D2 = P - D1.
In order for this to work, the NAS needs to know which block is missing. When you insert a new disk, it of course does know this, and it reconstructs all the data on it (including P blocks) from the other two.
mickle026 wrote:
...worse still if 2 fail?RAID-5 doesn't protect against two disk failures. RAID-6 will - and if you wish you could enable RAID-6 if you have 4 disks of the same size. With 4x2TB you'd only get 4 TB of data volume, and with the RN104 the write performance would be quite slow.
In any event, it is important to understand that RAID protection can and does fail. So you still need backups even with RAID.
- Thank you so much.
I have been networked since bnc and terminators, but I have to say although I knew of raid, I have never used it or had the need so never did any exploration of it.
I have always used network attached storage as mounted drives and used a custom data copy script as a backup.
I originally had no intentions of keeping backups of this data because it's not that important to keep, however now I'm pondering it. I never had more than 4 machines in my network, but now I have 9 it's starting to look like I might need raid one day.
Thank you so much for the information, I obviously have more reading to do on the subject.This is a good primer on RAID: http://www.thegeekstuff.com/2010/08/raid-levels-tutorial/
It doesn't cover RAID6 in the article, but just imagine RAID5 with an extra disk with another parity block stripe. There's a link to an additional article explaining RAID6 as well.
On a 4-bay NAS such as the 104, it probably makes more sense to have a 5th hard disk as a spare, sitting on the shelf as insurance, rather than run RAID-6. Set up email alerting and get timely notifications on drive failures. There is also a greater write penalty on RAID6 compared to RAID5, as there is the extra parity block write.
itsjasper wrote:
There is also a greater write penalty on RAID6 compared to RAID5, as there is the extra parity block write.
Yes. I wouldn't recommend RAID-6 on the RN104. The Q parity blocks are harder to compute than the simple XOR used for P, and there is a big performance hit.
Keeping a spare drive handy is a good strategy, as it can take a few days for a replacement to arrive.
And of course, backups...
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