《DataOntap核心技术》-课件设计（公开）.ppt

* * * * Unlike general purpose file systems, WAFL has an intimate understanding of its underlying physical disk configuration and is optimized for RAID. WAFL caches write operations that come in from the network, gathers them up, de-duplicates them, coalesces them, performs a single parity calculation, and then performs a massive stripe write across all the disks. The infrequency with which WAFL performs writes, coupled with the fact that it does a single massive parity calculation (versus a lot of little ones) combines to ensure the RAID parity disk does not become a bottleneck within the system (as it would typically do with a general purpose file system and conventional RAID 4). This behavior also contributes to superior read performance, since more of the disks’ operations-per-second potential is left over for reads. It contributes to reduced fragmentation because so much of a single file/LUN write is likely to be physically proximate on the disks. Question: How many RAID groups are supported on a single appliance? Answer: As many as 400 as of Data ONTAP 7.2.2. Question: How many disks can you have in a RAID group? Answer: It depends! - What platform? NearStore R200, FAS9xx, FAS2x0, FAS20x0, FAS30x0, FAS60x0? - single-parity RAID or RAID-DP? - What version of Data ONTAP? - Default, suggested max RAID group size, or actual max RAID group size? The answer is in the NOW documentation and will depend on answers to the above questions. For example, according to the Data ONTAP 7.2.2 Storage Management Guide (/NOW/knowledge/docs/ontap/rel722/pdfs/ontap/mgmtsag.pdf), the single-parity RAID group limits are: Platform Max group size Default group size Min group size FAS250 14 7 2all other systems 7 7 2(with SATA disks)all other systems 14 8 2(with FC disks) Question: Besides single- and double-parity RAID, does NetApp also support RAID 1 mirroring? Answer: Yes, and two ways. When creating what nominally would be a RAID 4 group, if you specify just 2 disks, D