Storage Understanding RAID10 - help..!

[AT0MAC]

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??

[tehBoris]

To expand a RAID at a later date you will either need to use a RAID controller that supports this or use a hardware RAID for both 1's then use software RAID for the 0.

Trouble is though, on a theoretical level, expanding a RAID 1 to RAID 10 is actually quite complicated if the 0 is stripped to boost performance. Spanned shouldn't be as much of a problem.

[AT0MAC]

Originally Posted by tehBoris

To expand a RAID at a later date you will either need to use a RAID controller that supports this or use a hardware RAID for both 1's then use software RAID for the 0.

Trouble is though, on a theoretical level, expanding a RAID 1 to RAID 10 is actually quite complicated if the 0 is stripped to boost performance. Spanned shouldn't be as much of a problem.

OK, as my build is software RAID'ed it is not possible, good to know


Another thing, 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?

[theshadow2001]

I wouldn't bother with any sort of RAID 0 on a server. Unless for some reason the performance boost was essential and even then... If I was to choose a RAID array given my storage requirements, I would look at the level of redundancy versus the cost of implementing it. Then decide which RAID offers the most suitable balance to my situation.

[AT0MAC]

Originally Posted by theshadow2001

I wouldn't bother with any sort of RAID 0 on a server. Unless for some reason the performance boost was essential and even then... If I was to choose a RAID array I would look at the level of redundancy versus the cost of implementing it. Then decide which RAID offers the most suitable balance to my situation.

OK, how about two RAID1 arrays of 2TB each instead?

One for video, one for everything else - also because I only have to spin up two drives versus all four every time anything is being accessed.

Already ordered two more Hitachi 5K3000 2TB drives a few hours ago, so in total will be 4 drives.

[theshadow2001]

I think RAID one is fine for a casual home server. I recommend the wikipedia entry on RAID arrays as it has the various options tabulated nicely, with all the formulas for fault tolerance, space efficiency etc. I think its one of the better wikipedia articles I have seen actually.

[Margon]

I wouldnt use a 2tb and a 3tb drive in the same array as the array will use space off all the drives equivalent to the smallest drive, which is why in arrays its best to use disks of the same size.

[AT0MAC]

Originally Posted by Margo Baggins

I wouldnt use a 2tb and a 3tb drive in the same array as the array will use space off all the drives equivalent to the smallest drive, which is why in arrays its best to use disks of the same size.

I know it's not ideal, but that's how it is as I already have a 2TB and a 3TB drive...

[narwen]

What operating system?

[Margon]

Originally Posted by AT0MAC

I know it's not ideal, but that's how it is as I already have a 2TB and a 3TB drive...

then do raid 5 with the 3 2tb disks giving you a 4tb array and use the 3tb as a stand alone drive.

[AT0MAC]

Originally Posted by Margo Baggins

then do raid 5 with the 3 2tb disks giving you a 4tb array and use the 3tb as a stand alone drive.

I am a hardcore mac user, so my server will run OSX Server and therefor no RAID5 options.

I am now thinking of running two RAID1 arrays, one for video via Plex and another for music in serviio. I intend to invest in some Linn or NAD Master series DLNA players and a few Roku video players so I guess the plex app is a little nicer for vids were the serviio is more allround for music.

[scott_chegg]

Just remember RAID only protects you against disk failure and not against data corruption so is not a replacement for backups.

[mm vr]

RAID5 allows one disk in the array to fail without data loss, RAID6 allows two disk failures. RAID1 allows half of the disks to fail, but I'm not entirely sure if RAID1 is supported for more than two disks.

We have a critical database server at work that runs RAID1. Both drives failed, and backups had also failed for some reason. We ended up with a €10k bill for data recovery. So yeah, RAID is not backup.

[saspro]

Originally Posted by AT0MAC

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

RAID 10 is great for servers. RAID 50 is better but RAID 10 works.
RAID 10 OS & database areas then RAID 6 storage areas.

[Guinevere]

Originally Posted by AT0MAC

As I see it RAID1 gives security and double the read speed but have

Where have you seen evidence that OSX Raid1 will improve throughput? It's normal (and logical) that software raid degrades performance rather than improve it.

And no raid1 does not provide 'security' it protects you from one particular type of hardware failure without offering protection to the other types of data loss / corruption.

You haven't told us what you're using the array for, so my comments are based on 'average' usage.

I would most certainly not recommend using Raid 10. Ever.

Scenario 1 : You need real time redundancy of your data, zero downtime (or close to it) and you're changing gigabytes of data per hour and can't afford to lose an hours worth of work:
Use Raid 1 for your live data, and perform either a time machine or CCC backup to second + third drives. These can be independent to give you two independent backups, or paired in Raid 1. (I'd use TM for one and CCC for the other)

Scenario 2 : You're changing gigabytes of data per hour but are okay with hourly backups
Don't use raid. Work off one drive and use Time Machine to backup to a second drive

Scenario 3 : You changing megabytes of data per hour and want real time backups
Work off one drive. Use dropbox for cloud backups (or your cloud backup tool of choice) and then use time machine / CCC for local backups.

Here's what I do...
I work off a super fast 512GB SSD
For data that doesn't require so much speed I have a 256GB SSD attached via USB 3.0
For data that needs even less speed I have a 1TB HDD attached via USB 3.0
Backups of all my working data (that is data which changes while I'm working) are made using dropbox where I have a 100GB account.
Hourly backups are performed using Time Machine which alternates between two drives.
In the event of hardware failure I can have near zero downtime by using a spare machine and moving my data around.

[AT0MAC]

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?

[mm vr]

Originally Posted by AT0MAC

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.

Unfortunately it doesn't work like that. The speed will be the same as with a single drive. (How would reading the SAME data in two places be faster? )

RAID1 will also only protect from a drive failure. If you (or a virus or something) accidentally deletes important files, they are immediately gone from both drives.

[AT0MAC]

Originally Posted by mm vr

Unfortunately it doesn't work like that. The speed will be the same as with a single drive. (How would reading the SAME data in two places be faster? )

RAID1 will also only protect from a drive failure. If you (or a virus or something) accidentally deletes important files, they are immediately gone from both drives.

Ok, so there is no speed difference - never mind. (but according the great wiki article of the subject: "Since all the data exists in two or more copies, each with its own hardware, the read performance can go up roughly as a linear multiple of the number of copies. That is, a RAID 1 array of two drives can be reading in two different places at the same time"

RAID1 for drive failures yes, Clone of that for RAID failures (as in if the software suddenly decide it needs a rebuild and accidentally deletes data), TImeMachine for file corruption - and cloud backup to secure against virus infected files (could just scan, eliminate the thread and redownload the implicated files).

So - is my plan good or you have a better option for a bullet proof data server?

[mm vr]

For a bullet proof setup you should also consider events like burglary and fire. The internet backup solution you have there should do pretty well for that.

[Atomic]

Originally Posted by mm vr

Unfortunately it doesn't work like that. The speed will be the same as with a single drive. (How would reading the SAME data in two places be faster? )

You've got it wrong here. Since both disks hold the same data, you can read the file in two places at once.

Say a file contains four 'chunks' A/B/C/D, here's how they would be read in different setups:

Single Disk would read each in turn: (*it might skip about due to the disk intelligent read but I'm going to simplify this.)

Time: 1-2-3-4
Disk: A/B/C/D

RAID1 would be able to read the file in two places simultaneously

Time:  1-2-3-4
Disk1: A/C/-/-
Disk2: B/D/-/-

You can see that RAID1 could in theory read the data twice as fast. Due to other factors it's not actually twice as fast but it's just an rough illustration.