As for conversion between RAID levels; usually dump and restore are your best bet. Even if your controller HBA supports a RAID level migration; for a small array hosted in a server, dump and restore is your least risky bet for successful execution; you really need to dump anyways, even on a controller that supports clever RAID level migrations (The ServeRaid does not fall into this category), there is the possibility that the operation fails, leading to data loss, so backup first. On Wed, Dec 10, 2014 at 2:49 AM, Seth Mos <seth.mos@dds.nl> wrote:
symack schreef op 9-12-2014 22:03: [snip] Raid10 is the only valid raid format these days. With the disks as big as they get these days it's possible for silent corruption.
No! Mistake. It depends. RAID6, RAID60, RAID-DP, RAIDZ3, and a few others are perfectly valid RAID formats, with sufficient sparing. You get fewer extra average random write IOPS per spindle, but better survivability, particularly in the event of simultaneous double failures or even a simultaneous triple-failure or simultaneous quadruple failure (with appropriate RAID group sizing), which are not necessarily as rare as one might intuitively expect. And silent corruption can be addressed partially via surface scanning and built-in ECC on the hard drives, then also (for Non-SATA SAS/FC drives), the decent array subsystems low-level formatted disks with larger sector size at the time of initialization and slip in additional error correction data within each chunk's metadata, so silent corruption or bit-flipping isn't necessarily so silent on a decent piece of storage equipment. If you need to have a configuration less than 12 disk drives, where you require good performance for many small random reads and writes, and only cheap controllers are an option, then yeah you probably need Raid10, but not always. In case you have a storage chassis with 16 disk drives, an integrated RAID controller, a solid 1 to 2gb NVRAM cache and a few gigabytes read cache, then RAID6 or RAID60, or (maybe) even RAID50 could be a solid option for a wide number of use cases. You really just need to calculate an upper bound on the right number of spindles spread over the right number of host ports for the workload adjusted based on which RAID level you pick with sufficient cache (taking into account the caching policy and including a sufficiently large safety factor to encompass inherent uncertainties in spindle performance and the level of variability for your specific overall workload). -- -JH