From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Davidsen Subject: Re: recommendations for stripe/chunk size Date: Wed, 06 Feb 2008 17:37:18 -0500 Message-ID: <47AA369E.2090501@tmr.com> References: <20080206202536.3316124D1D@gemini.denx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080206202536.3316124D1D@gemini.denx.de> Sender: linux-raid-owner@vger.kernel.org To: Wolfgang Denk Cc: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= , linux-raid@vger.kernel.org List-Id: linux-raid.ids Wolfgang Denk wrote: > In message <47AA08E7.5000801@tmr.com> you wrote: > >>> I actually think the kernel should operate with block sizes >>> like this and not wth 4 kiB blocks. It is the readahead and the elevator >>> algorithms that save us from randomly reading 4 kb a time. >>> >>> >>> >> Exactly, and nothing save a R-A-RW cycle if the write is a partial chunk. >> > > Indeed kernel page size is an important factor in such optimizations. > But you have to keep in mind that this is mostly efficient for (very) > large strictly sequential I/O operations only - actual file system > traffic may be *very* different. > > That was actually what I meant by page size, that of the file system rather than the memory, ie. the "block size" typically used for writes. Or multiples thereof, obviously. > We implemented the option to select kernel page sizes of 4, 16, 64 > and 256 kB for some PowerPC systems (440SPe, to be precise). A nice > graphics of the effect can be found here: > > https://www.amcc.com/MyAMCC/retrieveDocument/PowerPC/440SPe/RAIDinLinux_PB_0529a.pdf > > I started that online and pulled a download to print, very neat stuff. Thanks for the link. > Best regards, > > Wolfgang Denk > > -- Bill Davidsen "Woe unto the statesman who makes war without a reason that will still be valid when the war is over..." Otto von Bismark