If that ratio is mostly pointing towards misaligned I/Os, we have occasionally seen performance impact in the past, due to increased locking activity in the array cache elements (slots). What may cause an effect, is the ratio between misaligned I/Os and the overall number of I/Os. It can happen at times, and despite its unlucky name, it is not a functional error as such. the cache slot size of the array being 128 KiB on a PowerMax sufficiently explains a higher number of misaligned I/Os seen on the hosts using SFW.Ī misaligned I/O is a terminology that Dell uses to describe a situation where a data entity that is written to disk, blocks more array cache slots, than the entity size would formally require. However, in general, it follows from that definition, that a misalignment is an expected behavior. The difference between the offset of the volume on the disk being at 32 KiB vs. For a 512-byte FBA disk, the 64 block settings results in an offset of 32 KiB. In the history of the array (Symmetrix > DMX > VMAX > PowerMax), internal cache block size has changed twice, now being at 128 KiB. The volume offset in the product (SFW) is set in blocks. A Symmetrix type disk includes PowerMax arrays. The default offset for InfoScale Storage foundation for Windows (SFW) 8.0 and before is "64" for a "Symmetrix" type disk.
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