Software vs Hardware RAID

[Grant M.]

The difference between hardware & software RAIDS is tremendous, and the 
difference between Software RAIDs & Software RAIDs, and Hardware RAIDs & 
Hardware RAIDs is also pretty substantial.

Software RAIDs:
   o simple meta-devices that allow for striping & mirroring (RAID0 & 1)
       o Solaris MD & Linux LVM
   o logical volume managers (LVMs)that allow for disk-swapping & RAID5
       o Apple OSX Server Disk Utility?
   o more elaborate LVMs that manage disk pools, snapshots, & corruption
       o Solaris ZFS

Hardware RAIDs:
   o simple RAID cards or onboard RAID controllers for stripes & mirrors
       o RAID0, RAID1, RAID1+0
   o more elaborate RAID controller cards
       o RAID0, 1, & 5
       o maybe hot swap or global spare disks
   o standard Enterprise RAIDs
       o RAID0, 1, & 5, hot-swappable disks, controllers
       o Fiber-channel controllers or backplanes/disks
       o maybe SaS disks (Serial-attached SCSI)
       o luns, partitions
   o Advanced Enterprise RAIDs
       o same as above, but with 4gb interfaces & RAID6, 50 & 60
       o host-to-lun mapping, and perhaps some SAN functionality
       o everything except enclosure hot-swappable

This list is _really_ simplified, and the range of available 
functionality is very generalized.

In reality each product is different from the rest, and you really need 
to assess what your needs and desires are for the specific goal you are 
trying to achieve. I usually recommend that you base your decision 
partly on what the acceptable downtime is, and what that amount of 
downtime of the system will cost your company. If it's going to cost you 
tens of thousands to be down for half a day, then to spend $10k or more 
on a reliable, high-availability RAID is not unacceptable. You also need 
to assess what the application is, as databases, file services, and 
application services all have different requirements.

As a note, Apple's OSX Leopard is supposed to include the ZFS 
filesystem/LVM. That should be an incredible improvement from the HFS+ 
system that is being employed presently.

Grant M.
-- 
Grant Mongardi
Senior Systems Engineer
NAPC

gmongardi-cGmSLFmkI3Y at public.gmane.org
http://www.napc.com/
781.894.3114 phone
781.894.3997 fax

NAPC | technology matters


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