Configuration for Open Source Operating systems with the SAM-SD Approach
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@GotiTServicesInc said:
I feel like RAID 5/6 might be pointless? Sure you can support 1 to 2 failed drives in each hardware array, but considering you are supporting multiple software arrays this might just be extra overhead with no real benefit? or maybe the rebuild time on a big RAID 5/6 array is worth having this fail safe in place?
RAID 5 almost never makes sense unless these are SSDs. RAID 6 will often make sense because the cost of rebuilding a full node, depending on what your cluster is, might be horrific. So often that is done not to protect against data loss but to protect against performance or availability loss.
But again, cluster specifics are required.
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I wasn't too sure, I figured depending upon your needs, that would dictate how many SANs in a cluster and what RAID/ non RAID setup you'd go with
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In my research I may have confused dual channel raid controllers with dual controllers. I know for current leads in our company they're requesting a dual controller box, but being that this box is operating by itself I'm assuming with the additional controller they're buying a bit more redundancy for that.
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@GotiTServicesInc said:
I wasn't too sure, I figured depending upon your needs, that would dictate how many SANs in a cluster and what RAID/ non RAID setup you'd go with
Typically SAN come in three forms:
- Single SAN, no replication. Just a server sharing out block storage.
- Dual SAN, replicated. If the master fails the slave takes over. Data is mirrored.
- Scale Out SAN. RAID does not apply as you are using RAIN.
Those are really the only models. The idea of large SAN clusters, while theoretically possible, using local RAID and network RAID to replicate the storage, effectively does not exist as it would be impractical. You'd be limited to RAID 1 meaning the more SANs you add you would become more reliable but you'd never be able to scale up. So put in 10 SANs with 100TB each and you'd still only have 100TB to use. No matter how many SANs you add to the cluster, you'd never get more than 100TB to use.
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@GotiTServicesInc said:
In my research I may have confused dual channel raid controllers with dual controllers.
Definitely different things. One is more or less just for SAS level channel throughput. The other is for redundancy at the controller level (in theory.)
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@scottalanmiller said:
@GotiTServicesInc said:
In my research I may have confused dual channel raid controllers with dual controllers.
Definitely different things. One is more or less just for SAS level channel throughput. The other is for redundancy at the controller level (in theory.)
Yeah I think I just had a brain fart when going over that, I understand the differences between it but got lost in the sauce swimming between the two topics heh
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so really a HA SAN for an enterprise wouldn't really be more than 2 ish SANs? And more than that you would go for more of a RAIN setup?
I figured duplication over a network even with 40GB pipes would still be painful but wasn't sure
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@GotiTServicesInc said:
I know for current leads in our company they're requesting a dual controller box, but being that this box is operating by itself I'm assuming with the additional controller they're buying a bit more redundancy for that.
You don't do dual controllers for protection, not in the real world. RAID controllers do very bad things when you pair them up, that's why enterprise servers don't ship that way, ever. Not even $100K servers are like that. And that's why dual controllers in SMB range SANs are bad, they actually cause outages rather than protecting against it.
One of the most important reads here is: Understanding the Relationship of Reliability and Redundancy
Reliability is the goal, redundancy is a tool. In this case, your redundancy would not support your goal so isn't a viable option.
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In your OP you said dual SAS controllers, that is how this is handled for high end enterprise servers $50K and up. The high end doesn't use RAID controllers at all, only SAS. SAS controller with software RAID can do the redundancy that can't be done with what is on the market for RAID controllers well.
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I assumed SAS has built in raid which I realize now was a bad assumtion. dual controllers would just be used to increase the number of drives you could stick in a box then which makes more sense.
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@GotiTServicesInc said:
so really a HA SAN for an enterprise wouldn't really be more than 2 ish SANs? And more than that you would go for more of a RAIN setup?
Correct, enterprise SANs have traditional always been "scale up" or "vertical scaling" devices. Your size is determined by how big a single SAN can go. HA is provided by a combination of mainframe class design and features and mirroring to a second SAN. That's all we've ever had traditionally.
Moving to scale out systems is very and very niche still. Using scale out with SAN is still relatively rare and problematic. The first vendors are just starting to get their footing on this and there are generally performance issues.
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@scottalanmiller said:
In your OP you said dual SAS controllers, that is how this is handled for high end enterprise servers $50K and up. The high end doesn't use RAID controllers at all, only SAS. SAS controller with software RAID can do the redundancy that can't be done with what is on the market for RAID controllers well.
So with the OP, would the question be more like, which RAID level should I use over all theses drives in software, vs one controller RAIDed against the other controller?
And would a SAM-SD really look at skipping hardware RAID for software?
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I did skim that but wasn't sure where the risk vs. reward scale crossed in regards to RAID
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@GotiTServicesInc said:
I assumed SAS has built in raid which I realize now was a bad assumtion. dual controllers would just be used to increase the number of drives you could stick in a box then which makes more sense.
SAS and SATA are the protocols that storage uses to communicate. RAID controllers talk SAS and/or SATA, but most controllers do this without having hardware RAID.
You don't use multiple controllers for more drives. There isn't any normal server on the market that goes beyond what a single controller can handle. A single good controller will do hundreds of drives.
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@Dashrender well, if it's not running other apps on the OS why save the CPU with a RAID card?
edit: I just realized you were tl;dr'ing, sorry - this post was for OP
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@Dashrender said:
@scottalanmiller said:
In your OP you said dual SAS controllers, that is how this is handled for high end enterprise servers $50K and up. The high end doesn't use RAID controllers at all, only SAS. SAS controller with software RAID can do the redundancy that can't be done with what is on the market for RAID controllers well.
So with the OP, would the question be more like, which RAID level should I use over all theses drives in software, vs one controller RAIDed against the other controller?
And would a SAM-SD really look at skipping hardware RAID for software?
That may have been more of what I was looking for but didn't know how to ask the question
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so why do they make boxes with dual controllers in them then ? I'm referring to your favorite, Nexsan @scottalanmiller
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@GotiTServicesInc said:
so why do they make boxes with dual controllers in them then ? I'm referring to your favorite, Nexsan @scottalanmiller
This seems like an obvious answer - which I'm going to say is money- because they can sell them. But I'm sure Scott will correct me if I'm wrong on that.
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So a brief Introduction to Hardware and Software RAID.
Pretty much you use hardware RAID when...
- you run Windows, HyperV or ESXi on the bare metal.
- you want blind drive swaps in a datacenter.
- you lack the operating system and/or software RAID experience or support to use software RAID.
- you just want a lot of convenience.
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Reasons 1 and 2 (OS/HV choice and blind drive swaps) represent nearly every case as to why hardware RAID is chosen and legitimately make hardware RAID a nearly ubiquitous choice in the SMB.
