NAS Advise/Raid 10 with 5 drives

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macuser

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#173180 14-May-2015 11:18

Hey about to go pickup a Synology DS1515+ tomorrow, it is a 5 bay NAS box.

I'm going to run RAID 10 as it is more redundant and better suited as a backup for our photography studio.

I was thinking of putting in 5 4TB WD REDS, with 4 running in raid 10, and one in hot spare for failure protection. Will this work?

Or is that bay more for SSD cache, or for RAID 5?

Is it worth buying the 5th HDD? We've already prepared to buy 5, but if the device doesn't support using the 5th drive to replace one that has failed, then there is no point.

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#1305022 14-May-2015 11:26

As per the specs on Synologys website, yes it does support hot spare in RAID10. Although personally I'd go for RAID6 unless you really need the write performance.

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#1305079 14-May-2015 12:25

I am running two Synology DS1515+ boxes, both with 5 x 6TB WD Reds, using RAID 5.
Fast, quiet, and totally reliable.
I haven't tried RAID 6.

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macuser

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#1305096 14-May-2015 12:56

Sideface: I am running two Synology DS1515+ boxes, both with 5 x 6TB WD Reds, using RAID 5.
Fast, quiet, and totally reliable.
I haven't tried RAID 6.

Awesome, would love to go to 6TB drives, but they're so much more expensive than 4TB drives

Dynamic

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#1305102 14-May-2015 13:04

Sideface: I am running two Synology DS1515+ boxes, both with 5 x 6TB WD Reds, using RAID 5.
Fast, quiet, and totally reliable.
I haven't tried RAID 6.

Sideface I expect knows his RAID levels, but not all of us do.

As hard drives get larger and larger, the speed of reading and writing to these drives is not keeping up. For example as time ticks by and we get drives with 4x greater space, we might only be reading and writing at 2x the speed.

As a consequence of this, when a RAID drive fails, it is taking longer than it used to for the RAID to repair/rebuild. During this item the remaining drives are under greater stress and therefore they are more likely to fail. I can't give you any firm numbers on this.

RAID10 with 4 drives will continue with 1 drive failure, and possibly a second failed drive depending on where that second drive sits in the array. RAID10 with 6 disks means you might be able to lose up to 3 disks without losing data (if the 'right' disks fail).

RAID5 permits only one drive failure. A second drive going down loses the whole array and its data.

RAID6 extends RAID5 by introducing a second parity drive allowing for 2 drives to fail and the array keeps going. If you have a fast controller, RAID6 can be as fast as RAID10 IIRC. A slow controller means RAID5/6 perform poorly due to the parity calculation.

RAID6 is more space-efficient when you have 5 or more drives. RAID10 gives you only half of the capacity of all of your drives as usable space. RAID6 gives you the capacity of your drives, minus the two used for the parity.

So a 5 disk RAID6 gives you 3 disks worth of usable space. The 4 disk RAID10 plus 1 Hot Spare gives you only 2 disks worth of space. In an ideal world I woudl encourage you to try one then the other and see if the RAID6 performance is good enough for you to enjoy the larger available space.

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macuser

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#1305107 14-May-2015 13:09

Dynamic:
Sideface: I am running two Synology DS1515+ boxes, both with 5 x 6TB WD Reds, using RAID 5.
Fast, quiet, and totally reliable.
I haven't tried RAID 6.

Sideface I expect knows his RAID levels, but not all of us do.

As hard drives get larger and larger, the speed of reading and writing to these drives is not keeping up. For example as time ticks by and we get drives with 4x greater space, we might only be reading and writing at 2x the speed.

As a consequence of this, when a RAID drive fails, it is taking longer than it used to for the RAID to repair/rebuild. During this item the remaining drives are under greater stress and therefore they are more likely to fail. I can't give you any firm numbers on this.

RAID10 with 4 drives will continue with 1 drive failure, and possibly a second failed drive depending on where that second drive sits in the array. RAID10 with 6 disks means you might be able to lose up to 3 disks without losing data (if the 'right' disks fail).

RAID5 permits only one drive failure. A second drive going down loses the whole array and its data.

RAID6 extends RAID5 by introducing a second parity drive allowing for 2 drives to fail and the array keeps going. If you have a fast controller, RAID6 can be as fast as RAID10 IIRC. A slow controller means RAID5/6 perform poorly due to the parity calculation.

RAID6 is more space-efficient when you have 5 or more drives. RAID10 gives you only half of the capacity of all of your drives as usable space. RAID6 gives you the capacity of your drives, minus the two used for the parity.

So a 5 disk RAID6 gives you 3 disks worth of usable space. The 4 disk RAID10 plus 1 Hot Spare gives you only 2 disks worth of space. In an ideal world I woudl encourage you to try one then the other and see if the RAID6 performance is good enough for you to enjoy the larger available space.

Thanks for the indepth reply.

I figure though that if S*** hits the fan and the device itself fails, I can pull drives out of RAID 10 and pretty easily read them from a regular computer?

That would be my other concern, device failure.

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#1305121 14-May-2015 13:25

macuser: I figure though that if S*** hits the fan and the device itself fails, I can pull drives out of RAID 10 and pretty easily read them from a regular computer? That would be my other concern, device failure.

Almost no chance of that in my experience.

The RAID10 will split files across multiple drives, so tyou'll be recovering chunks of files by looking at one disk, not whole files.

The file system the device uses is a Linux EXT4 system (which can be read by Windows but only after installing some additional software and I have not done this with drives greater than 500Gb).

If you set up two RAID1 (mirror disk) arrays then Disk1 will have data and Disk2 will mirror this. You can pull Disk1 out of the device and put it in a Windows computer, and then install the EXT3 file system driver to PROBABLY read the files. You would also have Disk3 and Disk4 as mirrors of each other in a separate RAID1 array. And Disk 5 would be the Hot Spare to leap in should any of the other disks fail.

If you want recoverability by way of easy reading in a Windows system, you might be better to have a low-powered Windows machine sitting in a corner using a tower case that can hold your 5 disks. We can assist with this on a professional basis if you are in Auckland. Windows 7/8 run very reliably as basic file servers if nobody fiddles with them.

Finally if you are buying the Synology from <popular local computer hardware discount chain>, quadruple-check the warranty. We have had 2 clients return faulty NAS devices, only to be told the device would have to be sent internationally for repair (as it had been parallel imported) and would be away 4-6 weeks. You can imagine how that went down with the clients! Note in both cases these NAS devices had been purchased prior to our working with these clients.

Cheers
Mike

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macuser

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#1305127 14-May-2015 13:35

Dynamic:
macuser: I figure though that if S*** hits the fan and the device itself fails, I can pull drives out of RAID 10 and pretty easily read them from a regular computer? That would be my other concern, device failure.

Almost no chance of that in my experience.

The RAID10 will split files across multiple drives, so tyou'll be recovering chunks of files by looking at one disk, not whole files.

The file system the device uses is a Linux EXT4 system (which can be read by Windows but only after installing some additional software and I have not done this with drives greater than 500Gb).

If you set up two RAID1 (mirror disk) arrays then Disk1 will have data and Disk2 will mirror this. You can pull Disk1 out of the device and put it in a Windows computer, and then install the EXT3 file system driver to PROBABLY read the files. You would also have Disk3 and Disk4 as mirrors of each other in a separate RAID1 array. And Disk 5 would be the Hot Spare to leap in should any of the other disks fail.

If you want recoverability by way of easy reading in a Windows system, you might be better to have a low-powered Windows machine sitting in a corner using a tower case that can hold your 5 disks. We can assist with this on a professional basis if you are in Auckland. Windows 7/8 run very reliably as basic file servers if nobody fiddles with them.

Finally if you are buying the Synology from <popular local computer hardware discount chain>, quadruple-check the warranty. We have had 2 clients return faulty NAS devices, only to be told the device would have to be sent internationally for repair (as it had been parallel imported) and would be away 4-6 weeks. You can imagine how that went down with the clients! Note in both cases these NAS devices had been purchased prior to our working with these clients.

Cheers
Mike

Yea we are going to purchase via PB tech so we will be very cautious, I initially thought of doing a NAS via a LSI card on a Win8 machine but I was concerned that it would get fiddled with. The Synology will be better at not being touched I feel.

Thanks so much for your advice!

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lxsw20

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#1305135 14-May-2015 13:42

RAID5 isn't recommended for anything over about 1TB disk IIRC, as it takes an age to rebuild and the chance of a rebuild failure becomes too high.

timmmay

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#1305136 14-May-2015 13:43

You need to back up your RAID array. A power surge could take the lot out. External disks are probably the most practical way. I've never found a tape system cheap enough for home use that's reliable, but I've never looked that hard.

Dynamic

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#1305137 14-May-2015 13:43

macuser: I initially thought of doing a NAS via a LSI card on a Win8 machine but I was concerned that it would get fiddled with. The Synology will be better at not being touched I feel. Thanks so much for your advice!

Good as gold. We have a couple of 'pc-as-a-nas' deployed. They have 2 cables - power and network - ad a password on the login so nobody on site can fiddle.

Good luck with the project. And remember RAID is not backup. :)

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Sideface

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#1305194 14-May-2015 14:48

Sideface: I am running two Synology DS1515+ boxes, both with 5 x 6TB WD Reds, using RAID 5. ...

Dynamic correctly points out that RAID is not backup - [EDIT] and that big RAID arrays take a long time to rebuild.

That's why I have two identical RAID 5 arrays in identical Synology DS1515+ boxes in different locations, each with its own APC UPS.

Array 1 is backed up to array 2 once a day.

I keep two spare WD Red HDDs (from the same batch as the RAID arrays) as replacements - but haven't needed them yet.

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Dynamic

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#1305198 14-May-2015 14:59

Sideface: Array 1 is backed up to array 2 once a day.

Nice setup.

What is your strategy for recovering an accidentally deleted/damaged/overwritten file that is not noticed for a day or two? Or are these boxes for archives for finished work only?

Wherever possible an offline backup si highly desirable in case corruption on NAS1 is replicated to NAS2. Stranger things have happened.

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Inphinity

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#1305203 14-May-2015 15:05

RAID6 is more consistently resilient than RAID10, although in larger deployments RAID10 is theoretically capable of higher resilience, in terms of number of failed disks, as Dynamic has pointed out above. If performance is relatively low on the priority (without being a not care factor) I would generally suggest RAID6 over RAID10 for a smaller deployment like 5 disks, as it will always (short of controller failure etc of course) survive two concurrent disk failures, where RAID10 may or may not survive 2 concurrent disk failures. Interestingly RAID10's probability of surviving multiple disk failures tends to increase as the number of disks in the array increase, due to the lower chance of both disks in a mirror pair being the failed ones, then decrease again as the number of unresolved failures rises due to the increasing chance of a pair failure.

Anyway, I would go RAID6. I'm fairly sure the DS1515+ is similar performance-wise to the RS2414+ and DS2415+ units we have at the moment, and they perform just fine with RAID5/6.

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#1305210 14-May-2015 15:22

Dynamic: .,.. What is your strategy for recovering an accidentally deleted/damaged/overwritten file that is not noticed for a day or two? Or are these boxes for archives for finished work only?

Wherever possible an offline backup is highly desirable in case corruption on NAS1 is replicated to NAS2. Stranger things have happened.

The two Synology DS1515+ boxes are for finished work only.
Mission-critical stuff (about 1% of files) is also on OneDrive.

But there is no protection from human stupidity - if I've accidentally deleted a file without noticing, and it's not still in the recycle bin, it's gone.

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#1305334 14-May-2015 17:58

Inphinity: RAID6 is more consistently resilient than RAID10, although in larger deployments RAID10 is theoretically capable of higher resilience, in terms of number of failed disks, as Dynamic has pointed out above. If performance is relatively low on the priority (without being a not care factor) I would generally suggest RAID6 over RAID10 for a smaller deployment like 5 disks, as it will always (short of controller failure etc of course) survive two concurrent disk failures, where RAID10 may or may not survive 2 concurrent disk failures. Interestingly RAID10's probability of surviving multiple disk failures tends to increase as the number of disks in the array increase, due to the lower chance of both disks in a mirror pair being the failed ones, then decrease again as the number of unresolved failures rises due to the increasing chance of a pair failure.

Anyway, I would go RAID6. I'm fairly sure the DS1515+ is similar performance-wise to the RS2414+ and DS2415+ units we have at the moment, and they perform just fine with RAID5/6.

RAID is part of it.

You can mirror+stripe the disks. That is disk redundancy.

But, resiliency is also dependent on the disk controller.

You need a high level RAID controller for higher RAID levels.

Your controller should have battery backup, static RAM etc., otherwise an OS crash, power crash etc.. can easily corrupt your disk array.

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