The Software RAID Inflection Point
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
But you can't just do that in the OS.
why not?
Because you don't know how it is being used. General purpose, remember?
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@dafyre said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@dafyre said in The Software RAID Inflection Point:
When mdraid detects a failed drive, kick off a script that fires off smartctl or ledctl or something?
To just signal the light?
Boy I would hope not - I think @dafyre is asking - why doesn't mdRAID have blind swap? What prevents it from kicking scripts off that light the light and demount the drive in preparation of being replaced?
Well, showing some lights is "easy", you just use the tools that are already there. What stops it from replacing the drive is what we keep saying... it doesn't have enough info to know what to do when a disk is replaced. It's a general purpose system, not a pre-defined NAS. Scripted MD is what almost all major NAS use, so obviously it works. But you can't just do that in the OS.
Now I get what Scott is saying... The NAS systems all have scripted checks for when you replace a drive in the system and such... Basically, the same commands that we would have to run by hand on a stock MD system... We should figure out how to do all this for ourselves in mdraid, lol.
Right, because you can choose your use case, but MD cannot do that on its own without significantly curtailing its functionality. MD offers way more options than a NAS device does, that's part of its power. If it did everything automatically, you'd give a lot of that up.
You could make an add on application that does lights and replacements automatically, of course, and I think in defining all of the things to detect and how to react you'd notice tonnes of "assumptions" that you have to make to make it all work.
But the MD guys would make setup scripts that ask the builder all those questions so that MD is setup as desired. Not unlike using a RAID card.
And then it would be limited in the same way, but even moreso, because it would have access to far more things.
-
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
-
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
Please help the feable with examples of things that would work in a different way, and why you would expect that to happen in a MD setup, but not in a RAID controller setup.
-
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
MD Relies on us to tell it how to operate. Part of that would be setting up the blinking lights and all of that too.
-
@dafyre said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
MD Relies on us to tell it how to operate. Part of that would be setting up the blinking lights and all of that too.
The limitations would only be in place AFTER we answered a bunch of questions, or set a bunch of settings making it become limited to those features. A RAID card isn't limited to what RAID levels it runs until we adopt the drives and set a RAID level. Now it's limited to that RAID level on that array. How is this different - again I feel there is some fundamental thing I'm missing.
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
Please help the feable with examples of things that would work in a different way, and why you would expect that to happen in a MD setup, but not in a RAID controller setup.
Floopy drive RAID array!
Ok, onto something a little more practical. Mirrored USB boot drives and a "normal" storage array. Or mirrored SD card storage. Lots of different things about that md just handles without muss or fuss.
-
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
Please help the feable with examples of things that would work in a different way, and why you would expect that to happen in a MD setup, but not in a RAID controller setup.
Floopy drive RAID array!
Ok, onto something a little more practical. Mirrored USB boot drives and a "normal" storage array. Or mirrored SD card storage. Lots of different things about that md just handles without muss or fuss.
I literally only see a string of words above.. they make no sense what so ever, and even less when trying to understand the MD managing drives.
I use MD to build an 8 drive array in my Dell server. A drive on slot 0 fails. Now what? MD can't be made smart enough to make the BIOS/UEFI blink the light and unmount the drive? If it can't why not? Again I'm clearning missing something.
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
Please help the feable with examples of things that would work in a different way, and why you would expect that to happen in a MD setup, but not in a RAID controller setup.
RAID controller makes assumption, like you are replacing the failed drive. MD doesn't know if you are starting to build a new array, for example, or if the drive is not meant for part of that array. The RAID controller is limited, it only sees disks meant for its arrays. MD sees every device on the system. Do you want MD RAID to automatically grab that USB Backup drive that you were busy using to recover critical documents and format it as part of your RAID 6 array? If not, why not?
-
@Dashrender said in The Software RAID Inflection Point:
Ok, onto something a little more practical. Mirrored USB boot drives and a "normal" storage array. Or mirrored SD card storage. Lots of different things about that md just handles without muss or fuss.
I literally only see a string of words above.. they make no sense what so ever, and even less when trying to understand the MD managing drives.
I use MD to build an 8 drive array in my Dell server. A drive on slot 0 fails. Now what? MD can't be made smart enough to make the BIOS/UEFI blink the light and unmount the drive? If it can't why not? Again I'm clearning missing something.
You are missing that your use case is just one of thousands for MD RAID and you can't assume it to be everyone's use case. Mirrored USB boot drives, SD cards and such are normal situations for MD RAID.
-
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
-
@scottalanmiller said in The Software RAID Inflection Point:
its arrays. MD sees every device on the system. Do you want MD RAID to automatically grab that USB Backup drive that you
Because you told it during setup to not do that. You told it during setup that in the case of failed drive that you would put the new drive in the old drives connection.
-
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
-
@Dashrender said in The Software RAID Inflection Point:
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
Or does a RAID card something else that I'm missing.
RAID card assumes you'll only attach things to it that you want to work in a specific way. MD can't do that.
Please help the feable with examples of things that would work in a different way, and why you would expect that to happen in a MD setup, but not in a RAID controller setup.
Floopy drive RAID array!
Ok, onto something a little more practical. Mirrored USB boot drives and a "normal" storage array. Or mirrored SD card storage. Lots of different things about that md just handles without muss or fuss.
I literally only see a string of words above.. they make no sense what so ever, and even less when trying to understand the MD managing drives.
I use MD to build an 8 drive array in my Dell server. A drive on slot 0 fails. Now what? MD can't be made smart enough to make the BIOS/UEFI blink the light and unmount the drive? If it can't why not? Again I'm clearning missing something.
You can automate that functionality if you want, but MD is not just about hard drives. Heck, you could use it with TAPE! You can't just automate it assuming hard drives are being used.
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
So do it. Nothing is stopping someone from automating the process. It's just never sold to someone like that.
-
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
So do it. Nothing is stopping someone from automating the process. It's just never sold to someone like that.
And the question is, why not?
Scott clearly loves software RAID - So why not make systems that automate this process based around limits you put in place? If something falls outside those limits, manual intervention will of course be required.
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
Right, but that's not logic that belongs in MD. That's for you to provide afterwards. That's a higher level function.
-
@Dashrender said in The Software RAID Inflection Point:
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
So do it. Nothing is stopping someone from automating the process. It's just never sold to someone like that.
And the question is, why not?
Scott clearly loves software RAID - So why not make systems that automate this process based around limits you put in place? If something falls outside those limits, manual intervention will of course be required.
Because there is generally too much desire for flexibility and in large shops there is no need for this and small ones there is no market pressure.
-
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
So do it. Nothing is stopping someone from automating the process. It's just never sold to someone like that.
And the question is, why not?
Scott clearly loves software RAID - So why not make systems that automate this process based around limits you put in place? If something falls outside those limits, manual intervention will of course be required.
Because there is generally too much desire for flexibility and in large shops there is no need for this and small ones there is no market pressure.
No market pressure in small shops because they just go hardware RAID instead?
-
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@travisdh1 said in The Software RAID Inflection Point:
@Dashrender said in The Software RAID Inflection Point:
@scottalanmiller said in The Software RAID Inflection Point:
RAID Hardware sees.... drives destined for RAID arrays. MD sees everything on the system. They are very different from that one perspective alone.
OK, great, I get that - but nothing stops you from saying, this array is these device only, and when a fail happens do x.
So do it. Nothing is stopping someone from automating the process. It's just never sold to someone like that.
And the question is, why not?
Scott clearly loves software RAID - So why not make systems that automate this process based around limits you put in place? If something falls outside those limits, manual intervention will of course be required.
Because there is generally too much desire for flexibility and in large shops there is no need for this and small ones there is no market pressure.
No market pressure in small shops because they just go hardware RAID instead?
Yup, they aren't looking for a solution like that. And it would be rather complicated because you still can't visually inspect for it and know that it is always going to be the same and so forth.
