Louwtjie Burger wrote: > On 11/8/07, Richard Elling <[EMAIL PROTECTED]> wrote: > >> Louwtjie Burger wrote: >> >>> Hi >>> >>> What is the impact of not aligning the DB blocksize (16K) with ZFS, >>> especially when it comes to random reads on single HW RAID LUN. >>> >>> >> Potentially, depending on the write part of the workload, the system may >> read >> 128 kBytes to get a 16 kByte block. This is not efficient and may be >> noticeable >> as a performance degradation. >> > > Hi Richard. > > The amount of time it takes to position the drive to get to the start > of the 16K block takes longer than the time it takes to read the extra > 112 KB ... depending where on the platter this is one could calculate > it. > > Also... doesn't ZFS do some form of read ahead .. 64KB anyways? > > I suspect that the reason for the blocksize allignment is not so much > for 50 IOP's ... I think it only shows its ugly head when your doing > 1000's of IOPs and the time it takes to read extra data starts adding > up. >
Yes, I agree. On a side note, we are starting to look much more closely at efficiency and trying to identify good ways to measure efficiency for the highly parallel systems of the present and future. The early work has been around power efficiency as the vendors berate each other as being power hungry. But we expect the efficiency improvements to continue across all aspects of computing. Hence the statement that reading extra stuff is inefficient, but not necessarily poorly performing :-) -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
