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I'm considering buying a ReadyNAS 628X and configuring it for RAID 10. To increase the reliability of the array, I've been thinking of using two drive vendors, populating it with HGST NAS disks and WD Reds.
Q1: What is the best way to interleave the disks such that Disk x of mirror 1 uses HGST and Disk x of mirror 2 uses WD? For a 628X, should the order of disks be: HGST, WD, HGST, WD and then WD, HGST, WD, HGST?
Q2: The HGSTs are 7200 RPM and the WDs are 5400 RPM. Is it a problem to mix drive speeds?
Q3: Does mixing drive vendors even matter? Should I just buy all WD Reds and be done with it?
Q4: Can I use 6 x 4TB WD Reds or 6 x 4TB HGST NAS disks in an old ReadyNAS Pro Business (if I upgrade it to OS 6)?
* RAID 5/6 is most dangerous when the array is degraded and rebuilding. That's exactly when the 2nd disk has failed in my two experiences. RAID 5/6 accelerates failure of remaining disks in a way that RAID-10 does not.
* RAID-10 will rebuild its array much more quickly -- since it just has to copy missing data from a disk in one mirror to the other.
* RAID-10 can survive a minimum of 1 disk failure up to N/2 disk failures. It's true that if one disk in both (RAID-10) mirrors fail simultaneously, the array is dead. But the chance that a second disk failure will take out the array should be 1/(n - 1)...
made me strongly consider RAID-10, especially the observation that "In raid 6, during a rebuild it has to read every drive and recalculate the missing data.That means you have to read [potentially terabytes and terabytes] of data to rebuild that and hope a URE doesn't occur."
I'll start by saying the analysis in the "death of raid" articles seems too simplistic to me. They make it sound like every disk read is like playing Russian Roulette - one chance in 10**14 of the URE bullet exploding your data. I don't think UREs are like that. Disk failures have a cause, they aren't just random events. When a disk fails, the chance of URE rises to 100%. When it's starting to fail, it rises very quickly from 0 to a much larger value. It's not a static 1 in 10**14 crap shoot.
I also don't think RAID 5/6 resync accelerates failures, though it is true that rebuilding the array requires either reading or writing every sector in it. More on that below.
Rebuilding RAID-10 is easier because it only requires mirroring one existing disk. The array fails if that existing disk fails during resync - but the 1/(n-1) probability is misleading (and in my opinion incorrect). Your "accelerate failures" concept is grounded in the idea that heavy disk I/O will create a failure in one of the remaining disks. With RAID-10 resync, the source disk (and of course the new mirror) are the only two disks that experience heavy I/O. So if that idea is correct, then the disk most likely to fail is in fact the source disk of the mirror.
I'm not really sold on that concept though. I think that when disks begin to fail, sectors silently become unreadable or unwriteable. But (at least with my data) most of the sectors are only rarely read or written - so those failures aren't detected right away. Then when a disk is detected as having failed, you replace it - and then discover there's other failures you didn't know about when the raid resync reads (or writes) everything.
So I don't think the RAID resync creates the failures - I think most of the time it uncovers failures that have already occured. I run the scheduled maitenance functions to try and detect those failures early.
Another observation - RAID-6 rebuild can survive UREs when you replace a single disk (because it has dual redundancy). Where it breaks down is if you have two or more UREs in the same stripe.
In my own experience, the odds of losing a RAID-5 array during resync are fairly small - certainly it happens sometimes, but not that often. In fact, I've never lost one that way. But there's always some chance your RAID array will fail, no matter what RAID mode you use - the defense against that is to have backups.
But if I were trying to solve the issues you are worried about, I think I'd go with multiple RAID-1 volumes instead of RAID-10. The resync process is the same with multiple RAID-1 as it is with RAID-10. But recovering data from RAID-1 is much easier than recovering data any of the other RAID modes. Plus it'd be much easier to increase storage (since you'd only need to offload and restore 1/4 of the data).
@Retired_Member wrote:
Used WD in the past, but switched to HGST, which show 10 to 15% better performance. They are a bit warmer during standard operation, but give the higher throughput and are more reliable to my experience. Well, do not mix them with WD, though.
Again, it's fine to mix them - you just won't get the performance gain. You could of course mix the HGST with other enterprise class drives, and then you would get the performance improvement.
HGST drives have a good reputation, and as far as I can tell, the folks here who've used them are quite happy with them. Personally I've found the WD Reds to be quite reliable - one or two failures since I started using them back in 2012. At the moment I have 14 in service.
Re: Advice on mixing and interleaving disks, RAID 10?
My two cents regarding questions 1 to 3
As you want to be protected against your raid drive getting degraded under whatever circumstances you do not care which drive is causing the potential fault. The beauty of raid is to distribute the redundancy of your data across the array in a totally balanced way. So, there is no need to mix vendors. To my understanding it would be a disadvantage.
Just get 6 drives of the same vendor, type, size and in the best of all possible worlds same firmware, too.
Major benefits are:
- same hardware performance across the complete raid array
- just in case you want to hold a seventh spare drive sticking with the same vendor makes your live easier here.
Re: Advice on mixing and interleaving disks, RAID 10?
I am wondering why you are going with RAID-10. There is some performance gain, but XRAID single redundancy would give you more options to expand the array later. You won't see much performance difference if you are using gigabit ethernet.
Q1: What is the best way to interleave the disks such that Disk x of mirror 1 uses HGST and Disk x of mirror 2 uses WD? For a 628X, should the order of disks be: HGST, WD, HGST, WD and then WD, HGST, WD, HGST?
Unfortunately the NAS doesn't provide much information on the way drives are ordered in these more complex RAID modes. It'd be helpful if it did (as it matters if you are trying to understand your options when recovering from multiple disk failures). Hopefully someone from Netgear will chime in.
Q2: The HGSTs are 7200 RPM and the WDs are 5400 RPM. Is it a problem to mix drive speeds?
The system will work fine, but of course the performance is gated by the slowest disks. You likely will get a warning about it (which is safe to ignore).
Q3: Does mixing drive vendors even matter? Should I just buy all WD Reds and be done with it?
The theory behind mixing disk models is pretty simple. Without mixing, you buy the same disks at the same time from the same supplier, and put them in the same chassis with the same load (thanks to RAID). So it's plausible to think that there is some risk that multiple disks will fail in rapid succession.
It's debatable how big that risk is - I'm sure people here will have different views. Personally I just use the WD Reds. Either way, you need a backup of your data, as RAID isn't enough to keep is safe.
Re: Advice on mixing and interleaving disks, RAID 10?
Used WD in the past, but switched to HGST, which show 10 to 15% better performance. They are a bit warmer during standard operation, but give the higher throughput and are more reliable to my experience. Well, do not mix them with WD, though.
Re: Advice on mixing and interleaving disks, RAID 10?
Thanks, RolandWausE & StephenB.
Yes, I'm using Gigabit Ethernet.
Why RAID-10? I've been running XRAID-2 (RAID-6) for a while; it's saved me at least twice when I experienced two-disk failures. But everything I've read suggests RAID-6 is less safe as the number of disks or volume size increases.
I'm leaning toward RAID-10 for reliability, ease of data recovery and reasonable performance. RAID-6 has the advantage of maximizing disk space, but I'm willing to sacrifice disk space since resiliency is more important to me. Disk space is cheap now and disks so large, that growing the array horizontally over time (via X-RAID) isn't that important to me.
Based on what I've read:
* RAID 5/6 is most dangerous when the array is degraded and rebuilding. That's exactly when the 2nd disk has failed in my two experiences. RAID 5/6 accelerates failure of remaining disks in a way that RAID-10 does not.
* RAID-10 will rebuild its array much more quickly -- since it just has to copy missing data from a disk in one mirror to the other.
* RAID-10 can survive a minimum of 1 disk failure up to N/2 disk failures. It's true that if one disk in both (RAID-10) mirrors fail simultaneously, the array is dead. But the chance that a second disk failure will take out the array should be 1/(n - 1): 1/7 in an 8-disk array (according to:
made me strongly consider RAID-10, especially the observation that "In raid 6, during a rebuild it has to read every drive and recalculate the missing data.That means you have to read [potentially terabytes and terabytes] of data to rebuild that and hope a URE doesn't occur."
But I'm interested to hear about your experience and suggestions if you have a contrary opinion.
* RAID 5/6 is most dangerous when the array is degraded and rebuilding. That's exactly when the 2nd disk has failed in my two experiences. RAID 5/6 accelerates failure of remaining disks in a way that RAID-10 does not.
* RAID-10 will rebuild its array much more quickly -- since it just has to copy missing data from a disk in one mirror to the other.
* RAID-10 can survive a minimum of 1 disk failure up to N/2 disk failures. It's true that if one disk in both (RAID-10) mirrors fail simultaneously, the array is dead. But the chance that a second disk failure will take out the array should be 1/(n - 1)...
made me strongly consider RAID-10, especially the observation that "In raid 6, during a rebuild it has to read every drive and recalculate the missing data.That means you have to read [potentially terabytes and terabytes] of data to rebuild that and hope a URE doesn't occur."
I'll start by saying the analysis in the "death of raid" articles seems too simplistic to me. They make it sound like every disk read is like playing Russian Roulette - one chance in 10**14 of the URE bullet exploding your data. I don't think UREs are like that. Disk failures have a cause, they aren't just random events. When a disk fails, the chance of URE rises to 100%. When it's starting to fail, it rises very quickly from 0 to a much larger value. It's not a static 1 in 10**14 crap shoot.
I also don't think RAID 5/6 resync accelerates failures, though it is true that rebuilding the array requires either reading or writing every sector in it. More on that below.
Rebuilding RAID-10 is easier because it only requires mirroring one existing disk. The array fails if that existing disk fails during resync - but the 1/(n-1) probability is misleading (and in my opinion incorrect). Your "accelerate failures" concept is grounded in the idea that heavy disk I/O will create a failure in one of the remaining disks. With RAID-10 resync, the source disk (and of course the new mirror) are the only two disks that experience heavy I/O. So if that idea is correct, then the disk most likely to fail is in fact the source disk of the mirror.
I'm not really sold on that concept though. I think that when disks begin to fail, sectors silently become unreadable or unwriteable. But (at least with my data) most of the sectors are only rarely read or written - so those failures aren't detected right away. Then when a disk is detected as having failed, you replace it - and then discover there's other failures you didn't know about when the raid resync reads (or writes) everything.
So I don't think the RAID resync creates the failures - I think most of the time it uncovers failures that have already occured. I run the scheduled maitenance functions to try and detect those failures early.
Another observation - RAID-6 rebuild can survive UREs when you replace a single disk (because it has dual redundancy). Where it breaks down is if you have two or more UREs in the same stripe.
In my own experience, the odds of losing a RAID-5 array during resync are fairly small - certainly it happens sometimes, but not that often. In fact, I've never lost one that way. But there's always some chance your RAID array will fail, no matter what RAID mode you use - the defense against that is to have backups.
But if I were trying to solve the issues you are worried about, I think I'd go with multiple RAID-1 volumes instead of RAID-10. The resync process is the same with multiple RAID-1 as it is with RAID-10. But recovering data from RAID-1 is much easier than recovering data any of the other RAID modes. Plus it'd be much easier to increase storage (since you'd only need to offload and restore 1/4 of the data).
@Retired_Member wrote:
Used WD in the past, but switched to HGST, which show 10 to 15% better performance. They are a bit warmer during standard operation, but give the higher throughput and are more reliable to my experience. Well, do not mix them with WD, though.
Again, it's fine to mix them - you just won't get the performance gain. You could of course mix the HGST with other enterprise class drives, and then you would get the performance improvement.
HGST drives have a good reputation, and as far as I can tell, the folks here who've used them are quite happy with them. Personally I've found the WD Reds to be quite reliable - one or two failures since I started using them back in 2012. At the moment I have 14 in service.
