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Understand RAID10 - help..!

 
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AT0MAC
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PostPosted: Sun Nov 11, 2012 4:16 am    Post subject: Understand RAID10 - help..! Reply with quote

I am currently building a server, were I have a 2tb and a 3tb drive installed, next to a 64gb os ssd.
I want to build the data drives in RAID10, so I understand it's two RAID1's combined into one RAID0.

But do that mean I can start with one RAID1, later on expand with two more drives in a seperate RAID1 and then combine in RAID0 - without loosing data from the original RAID1 set???

The tricky part is what happens when I combine into RAID0, if it needs to clean all drives??
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ez061111
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PostPosted: Sun Nov 11, 2012 6:30 am    Post subject: Reply with quote

Your RAID controller will deal with it, be it software (Disk Utility or something like SoftRaid) or hardware. Disk Utility has always left me with corruption at some point, I know people that swear by SoftRaid.

You want to achieve this with only 2 disks of different size?
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AT0MAC
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PostPosted: Sun Nov 11, 2012 6:45 am    Post subject: Reply with quote

ez061111 wrote:
Your RAID controller will deal with it, be it software (Disk Utility or something like SoftRaid) or hardware. Disk Utility has always left me with corruption at some point, I know people that swear by SoftRaid.

You want to achieve this with only 2 disks of different size?


Right now I have 2 discs of not the same size, but if I choose to go the RAID10 route I will obviously have to buy two more drives.

So what I want to do now is using my 2TB and 3TB to make a 2TB RAID1 volume.
Then later add two 2TB drives and make a second RAID1 volume and in the same event add both RAID1s into one large RAID0 of 4TB in size - the question is when I push the button and initialize it as a RAID0 will it then delete the data on the original RAID1 set??
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ez061111
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PostPosted: Sun Nov 11, 2012 7:30 am    Post subject: Reply with quote

I don't know of any RAID utility that allows you to switch on the fly between different forms of RAID without the need of reinitializing. Particularly if you are wanting to create a stripe into the mix. SoftRaid 'might' allow it, but I don't know.
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AT0MAC
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PostPosted: Sun Nov 11, 2012 7:33 am    Post subject: Reply with quote

ez061111 wrote:
I don't know of any RAID utility that allows you to switch on the fly between different forms of RAID without the need of reinitializing. Particularly if you are wanting to create a stripe into the mix. SoftRaid 'might' allow it, but I don't know.


You just confirmed what people over at Bit-Tech also said Smile

Another question then:

some one told me RAID10 would be a bad idea for a server - what do people here think?


As I see it RAID1 gives security and double the read speed but have normal write speed, then when you have two of them in RAID0 you get quadruple the read speed and double the write speed + data backup of up to three drive failures in a four drive RAID10 (because loose one disc no harm, loose two discs on separate RAID1s no harm, loose three discs and data will remain unharmed on one disc).

Anything I have not understood or missed?

...wait, it's only two drive failures right? Because the two separate RAID1s is part of the same RAID0 and therefor have half a file each - so a long as one drive in each RAID1 die then everything is ok, if two drives in the same RAID1 die i'm screwed. Correct?


Last edited by AT0MAC on Sun Nov 11, 2012 7:45 am; edited 1 time in total
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ez061111
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PostPosted: Sun Nov 11, 2012 7:44 am    Post subject: Reply with quote

From what I've read, RAID 10 is a great option as it mixes not only redundancy but the speed of striping. But I suppose it comes down to what it's purpose is: for a serving a large database it's probably great, to run as a system perhaps not.
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PostPosted: Sun Nov 11, 2012 8:01 am    Post subject: Reply with quote

I think you are confusing the two, the 1 and 0 are going to be inherently different than the 10, as the 10 is the management of the two ideas together, not an additive of the two. For you to migrate to a RAID10 you will need to reformat all disks and let the controller run the show.

In a 4 disk system of RAID10, if you lose 3 disks, you're lost as no one disk has all the data. From what I understand it also depends on which disks you lose in a 4 disk system, a loss of two can be trouble as it is a mirror of stripes. If you lose the 2 disks that make up the mirror all is lost. It's still more realistic to have a only 1 disk failure and still keep your data intact.

The trick is to realize that the RAID itself is not going to save your data, it's the redundancy of that RAID that saves your data.
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AT0MAC
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PostPosted: Sun Nov 11, 2012 8:05 am    Post subject: Reply with quote

ez061111 wrote:
I think you are confusing the two, the 1 and 0 are going to be inherently different than the 10, as the 10 is the management of the two ideas together, not an additive of the two. For you to migrate to a RAID10 you will need to reformat all disks and let the controller run the show.

In a 4 disk system of RAID10, if you lose 3 disks, you're lost as no one disk has all the data. From what I understand it also depends on which disks you lose in a 4 disk system, a loss of two can be trouble as it is a mirror of stripes. If you lose the 2 disks that make up the mirror all is lost. It's still more realistic to have a only 1 disk failure and still keep your data intact.

The trick is to realize that the RAID itself is not going to save your data, it's the redundancy of that RAID that saves your data.


So for short, as soon as I experience the first drive failure I should buy a new drive because if yet another drive fails I am screwed - just like in a usual RAID1 setup but with the RAID0 benefits on top.


Back to the second question, is RAID10 a good option for a server?
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PostPosted: Sun Nov 11, 2012 8:32 am    Post subject: Reply with quote

Yes, I have a few RAIDs and 2 backups of each those RAIDs. I maintain the 3rd backup of my most critical RAID in a safety deposit box. When I've built a RAID I always factor in purchasing at least 2 extra drives of the same for the eventual failure: 4 disk RAID, purchase 6 (4 for RAID and 2 backup).

Software RAIDs seem more forgiving as far as not necessarily needing identical disks (manufacturer, size, etc). As i have said, the software RAIDS I have done in the past with Disk Utility always failed at some point and i finally gave up on them. SoftRaid seems to be more robust and has at least some modicum of support behind it from the manufacturer...but it does have a modest price and i have never used it.

The most important thing to remember is how important your data is and what the rebuild times are. I have one block of data that would take years of painstaking work to rebuild and it wouldn't be the same. Whether we are talking about photos, music, work data, etc, some of it may ultimately be irreplaceable.

AT0MAC wrote:
Back to the second question, is RAID10 a good option for a server?
Yes, if it fits your needs. It looks to have a good balance of speed and redundancy.
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AT0MAC
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PostPosted: Sun Nov 11, 2012 8:54 am    Post subject: Reply with quote

ez061111 wrote:
Yes, I have a few RAIDs and 2 backups of each those RAIDs. I maintain the 3rd backup of my most critical RAID in a safety deposit box. When I've built a RAID I always factor in purchasing at least 2 extra drives of the same for the eventual failure: 4 disk RAID, purchase 6 (4 for RAID and 2 backup).

Software RAIDs seem more forgiving as far as not necessarily needing identical disks (manufacturer, size, etc). As i have said, the software RAIDS I have done in the past with Disk Utility always failed at some point and i finally gave up on them. SoftRaid seems to be more robust and has at least some modicum of support behind it from the manufacturer...but it does have a modest price and i have never used it.


I see your point about buying additional discs, but as I have heard other people say, buying many discs in the same shipment is a bad idea - so to spread my fail rate I will wait a few months to buy more. I don't expect all discs to go dead in an instant.

Actually just ordered two more Hitachi 5K3000 drives, same series as the other I use, but will let the first 2TB and the 3TB be on separate RAID1s again to spread fail rates.

I see softRaid have a $129 price tag, which don't seem so bad if you say Disc Utility does a bad job of maintaining reliability - also, they say SoftRaid have a quick rebuild time, could be important the day everything goes down... Lastly, they have a 30day test period, so I might start off with them and see how things go, if everything is fine I will buy, if nothing seems to be of any difference I will reset and just use DU.
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AT0MAC
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PostPosted: Thu Nov 15, 2012 6:13 am    Post subject: Reply with quote

I have now understood the point. Raid10 is not what I want.

Actually the original reason for building a server is that I have had a Buffalo NAS, a Linksys NAS and latest a Verbatim - all have failed and broke down.
I want a reliable way of keeping my data so backup is the very most important!


Therefor, I have thought about this type of solution:




I RAID1 the two 2TB main drives, so even if one drive fail I still have a functional copy, also I get double the read speed because everything can be read via both drives simultaneously.

RAID1 is very reliable, but I can still have corruption’s that make the two drives out of sync and in need of a rebuild and I could potential loose data - so I will setup my third 2TB drive to make a full clone of the 2TB RAID1 system every once a day.

Now I have secured any drive errors and software errors, but what about single file corruptions, still a possible thread. So my 3TB drive will be used as TimeMachine both for the RAID but also for my SSD were the OS will be housed.

Speaking about the OS, I have ordered a 64GB USB3.0 Integral Xcel flash drive to have an external boot clone copy of my OS made once a day, just like on the internal drives.



What do you guys think, possible, reliable and a good solution?
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AT0MAC
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PostPosted: Sat Nov 17, 2012 1:10 pm    Post subject: Reply with quote

Sorry to say that I can't exactly make what I wanted, due to very limited space in my chassis - so was only able to fit in 2x2TB+1x3TB+64GB.

As in, one primary data drive of 2TB, one daily clone of that drive also of 2TB, hourly 3TB TimeMachine partitioned into two so it also covers the 64GB OS SSD. The OS SSD is then cloned once a day to an external 64GB USB3 stick.

Not really as good, but very damn close.

Covers data corruption due to the time machine, covers drive failure due to the clones and also already have a brand new 2TB spare drive in original box laying on it's shelf here at home for the event one of the 2TB drives gives up.

Not bad not bad...

But no RAID...


Anyway, thank you a bunch for ideas and input to my original question, you guys are awesome!

Smile
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