2010/3/16 John Sessoms <jsessoms...@nc.rr.com>: > > I should know this, but either I don't or I've completely forgotten it. > > How difficult is it to change the configuration of a RAID 5 from three disks > to four disks ... or from four to five ... once you have the data on there? > > For example, if I start with a three disk RAID 5 in a tower with room & > connections for six disks. After I save up a bit more money, I want to add a > fourth disk to the array, and later a fifth and sixth. > > How much hassle is it? Can I just add the disk and let the controller > automatically re-configure the stripes? Or am I going to have to back the > data up somewhere else temporarily and start over?
Good question - essentially it depends on what your RAID controller and what your operating system can do. In a nutshell your wallet is the answer :[ As a rule any controller except those to avoid at ANY cost will let you add disks to existing arrays up to the supported total. Cheap controllers will then allow you to create a new logical disk which can be presented to the operating system as a new volume on which you can create new partitions within OS supported parameters, i.e. max size, type and number of partitions, also, under Windoze you can modify the volume type from basic to dynamic and merge partitions but I would avoid that. Better controllers will let you add the new array member to an existing logical disk which is subsequently rebuilt, i.e. stripes are reconfigured. This is done from a controller management tool which will also manage OS access for that period so that no interfering access can occur. High end consumer and most current enterprise controllers will offer virtualized storage where you can just add and remove hardware as you go. Also, storage support of Windows 7 is really good, I have to say but IIRC varies bteween editions so that may be worth a look. I will see what I can come up with on that. Next, you need to choose between DAS (Direct Attached Storage), NAS (Network Attached Storage), and used/remarketed SAN (Storage Area Network), i.e. an enterprise product. NAS and SAN will sit on the network somewhere, DAS will sit under your desk unless it is attached via fibre optics. NAS is nice as there are also units you can attach to your HiFi system and use as time shift VCRs and so on. It all depends on what you want. DAS is cheaper. For the type of disks you have to go with what the controller supports. Some enterprise controllers and enclosures support SAS and SATA in the same for factor. Generally, SCSI and SAS mean longevity and bigger moolah as well as more flexibility. Relative to your levels of use SATA is perfectly fine though as you are not producing enterprise levels of mechanical stress so basically any type of disk will do. Just make sure you stay away from ATAPI/IDE. Also, if you go with SCSI or SAS, don't get disks smaller than approx. 120-150 GB as they are being discontinued. 300 GB to 1 TB is the current level there. SATA goes higher but that is perfectly normal seeing the lower build quality requirements and MTBF / MTBR (Mean Time Before Failure / Repair). There are many used enterprise NASs & SANs out there at very good prices with so many companies going belly up and that stuff is flexible as hell and built like a tank. Feel free to ask me about that. What you need to bear in mind is that enterprise units generally put out massive fan noise so you'll need somewhere to put them. Just make sure a matching HBA (Host Bus Adaptor) and (physical/logical) controller are included and get a big name such as HP, IBM, or perhaps recent Dell but I never quite trust them. For value, SuperMicro is great, they use mostly Intel made OEM parts which are quite OK but you have to expect to pay a premium on replacement disks later because used parts availability is less than for the others. HTH & feel free to ask Cheers Ecke -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
