Messages in this thread |  | | Date | Thu, 1 Mar 2001 16:02:01 +0000 | From | "Stephen C. Tweedie" <> | Subject | Re: Writing on raw device with software RAID 0 is slow |
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Hi,
On Thu, Mar 01, 2001 at 10:44:38AM -0500, Ben LaHaise wrote: > > On Thu, 1 Mar 2001, Stephen C. Tweedie wrote: > > > Raw IO is always synchronous: it gets flushed to disk before the write > > returns. You don't get any write-behind with raw IO, so the smaller > > the blocksize you write in, the slower things get. > > More importantly, the mainstream raw io code only writes in 64KB chunks > that are unpipelined, which can lead to writes not hitting the drive > before the sector passes under the rw head. You can work around this to > some extent by issuing multiple writes (via threads, or the aio work I've > done) at the expense of atomicity. Also, before we allow locking of > arbitrary larger ios in main memory, we need bean counting to prevent the > obvious DoSes.
Yep. There shouldn't be any problem increasing the 64KB size, it's only the lack of accounting for the pinned memory which stopped me increasing it by default.
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