On Sun, 1 Aug 2004, Gordon Henderson wrote: > On Sun, 1 Aug 2004, Mikael Abrahamsson wrote: > > And also because scsi drives can do tagged queueing which makes it more > > efficient to do a lot of smaller operations. Historically the SCSI drives > > also had more cache memory which helps the situation, and the scsi > > RAID controllers probably also had more cache memory on them (I know RAID > > systems that have gigabytes of cache memory). > > What I find amusing these days is trying to work out the "boundary" point > between a "traditional" server with an (external) RAID controller and say > a Linux server with software RAID in a purely fileserving environment (eg. > NFS/Samba, not used for local operations at all) ... Both systems as a > unit provide the same services - ie. filespace at the end of the Ether, > but what are the advantages of one over the other, and why would I ever > want a hardware RAID controller in a PCI slot in a Server PC? > > Discuss... ;-) Recently I did a survey of this very question (hardware vs. software RAID) based on the comments from this mailing list: Software -------- - CPU must handle operations - twice the I/O bandwidth when using RAID1 + non-proprietary disk format + open source implementation - limited or non-existent support for hot-swapping, even with SATA (see http://www.redhat.com/archives/fedora-test-list/2004-March/msg01204.html) - OS-specific format (can't be shared between Linux, Windows, etc.) + drives can be anything (ie. a mixture of SATA, PATA, Firewire, USB, etc.) - disk surface testing must be done manually (7/2004) - no bad block relocation (7/2004) - no parity verification (7/2004) - no mirror verification (7/2004) + reputedly, much better performance than hardware raid Hardware -------- + off-loads the CPU + I/O bandwidth needed on a RAID1 system is same as single disk - proprietary disk format (although limited drivers are available for Linux) - proprietary implementation + easy hot-swapping (some controllers even indicate the bad drive with an LED) + non-OS-specific (can share between Linux, Windows, etc.) - some features may not be supported on non-Windows operating systems + able to create logical disks that seem like physical disks to the OS + bad sector relocation (on the fly?) - drives must connect to the controller and all must be same type (e.g. SATA) + disk surface testing done automatically + automatic bad block relocation + parity verification + mirror verification - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
