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How to create Raid 5 config w/ 4.11
- Thread starter johyus
- Start date
Dell support should have a ton of useful info, but first step you need to decide is whether to use hardware of software RAID. With NetWare, I suggest you use hardware RAID and you won't have to do much on the OS end. (Below is a reprint of hw vs. sw RAID) Sorry about the formatting!
Hardware RAID
The hardware based system manages the RAID subsystem independently from the host and presents to the host only a single disk per RAID array. This way the host doesn't have to be aware of the RAID subsystems(s).
The controller based hardware solution
DPT's SCSI controllers are a good example for a controller based RAID solution.
The intelligent contoller manages the RAID subsystem independently from the host. The advantage over an external SCSI---SCSI RAID
subsystem is that the contoller is able to span the RAID subsystem over multiple SCSI channels and and by this remove the limiting factor external
RAID solutions have: The transfer rate over the SCSI bus.
The external hardware solution (SCSI---SCSI RAID)
An external RAID box moves all RAID handling "intelligence" into a contoller that is sitting in the external disk subsystem. The whole subsystem is
connected to the host via a normal SCSI controller and apears to the host as a single disk.
This solution has drawbacks compared to the contoller based solution: The single SCSI channel used in this solution creates a bottleneck.
4 SCSI drives can already completely flood a SCSI bus, since the average transfer size is around 4KB and the command transfer overhead -
which is even in Ultra SCSI still done asynchonously - takes most of the bus time.
Software RAID
The MD driver in the Linux kernel is an example of a RAID solution that is completely hardware independent.
However its application is limited, since it only provides RAID level 0, but not the levels 1 and 5. The author stopped working on this.
Adaptecs RAID controllers are another example, they have no RAID functionality whatsoever on the controller, they depend on external drivers
to provide all external RAID functionality.
They are basically only multiple single AHA2940 controllers which have been integrated on one card. Linux detects them as AHA2940 and treats
them accordingly.
Every OS needs its own special driver for this type of RAID solution, this is error prone and not very compatible.
Hardware vs. Software RAID
Just like any other application, software-based arrays occupy host system memory, consume CPU cycles and are operating system dependent. By
contending with other applications that are running concurrently for host CPU cycles and memory, software-based arrays degrade overall server
performance. Also, unlike hardware-based arrays, the performance of a software-based array is directly dependent on server CPU performance and
load.
Hardware RAID
The hardware based system manages the RAID subsystem independently from the host and presents to the host only a single disk per RAID array. This way the host doesn't have to be aware of the RAID subsystems(s).
The controller based hardware solution
DPT's SCSI controllers are a good example for a controller based RAID solution.
The intelligent contoller manages the RAID subsystem independently from the host. The advantage over an external SCSI---SCSI RAID
subsystem is that the contoller is able to span the RAID subsystem over multiple SCSI channels and and by this remove the limiting factor external
RAID solutions have: The transfer rate over the SCSI bus.
The external hardware solution (SCSI---SCSI RAID)
An external RAID box moves all RAID handling "intelligence" into a contoller that is sitting in the external disk subsystem. The whole subsystem is
connected to the host via a normal SCSI controller and apears to the host as a single disk.
This solution has drawbacks compared to the contoller based solution: The single SCSI channel used in this solution creates a bottleneck.
4 SCSI drives can already completely flood a SCSI bus, since the average transfer size is around 4KB and the command transfer overhead -
which is even in Ultra SCSI still done asynchonously - takes most of the bus time.
Software RAID
The MD driver in the Linux kernel is an example of a RAID solution that is completely hardware independent.
However its application is limited, since it only provides RAID level 0, but not the levels 1 and 5. The author stopped working on this.
Adaptecs RAID controllers are another example, they have no RAID functionality whatsoever on the controller, they depend on external drivers
to provide all external RAID functionality.
They are basically only multiple single AHA2940 controllers which have been integrated on one card. Linux detects them as AHA2940 and treats
them accordingly.
Every OS needs its own special driver for this type of RAID solution, this is error prone and not very compatible.
Hardware vs. Software RAID
Just like any other application, software-based arrays occupy host system memory, consume CPU cycles and are operating system dependent. By
contending with other applications that are running concurrently for host CPU cycles and memory, software-based arrays degrade overall server
performance. Also, unlike hardware-based arrays, the performance of a software-based array is directly dependent on server CPU performance and
load.
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