Date: Tue, 10 Dec 2002 07:08:15 +0100 From: Mark Rowlands <fuc952d@tninet.se> To: "Greg 'groggy' Lehey" <grog@FreeBSD.org> Cc: questions@FreeBSD.org Subject: Re: couple of vinum questions from a vinum newbie. Message-ID: <200212100708.15890.fuc952d@tninet.se> In-Reply-To: <20021208234555.GO96646@wantadilla.lemis.com> References: <200212081704.28492.fuc952d@tninet.se> <20021208234555.GO96646@wantadilla.lemis.com>
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On Monday 09 December 2002 12:45 am, Greg 'groggy' Lehey wrote: > On Sunday, 8 December 2002 at 17:04:28 +0100, Mark Rowlands wrote: > > I have decided to dip my toe into the vinum waters primarily for improved > > read performance, not redundancy or reliability. I have backups for that > > ;-). > > > > I have two questions, one related to optimal stripe size and one to > > gathering statistics. > > > > I have a freshly cvsupped 4.7 stable currently installed on a 30g single > > disk I propose to add a second 30gb disk as a mirror of this. and to add > > two new identical disks (maxtor fdb-9 120gb) and create a striped volume > > for data on those. > > > > I propose (maybe) to create a single striped volume but...... what stripe > > size? Reading the various vinum docs and looking at some of the samples > > I found lying around the web left me a touch confused. > > > > There are two categories of files on the data disk, largeish ( 4-5mb) > > which are most frequently accessed but the overwhelming majority of files > > are much smaller (<4k) but not accessed so frequently. > > > > So, is it better to try and optimize for the most frequently accessed, or > > the filesize that comprises the bulk of file accesses? or better to > > create two volumes with different stripe sizes. In either case, if anyone > > has any concrete recommendations, I would welcome them. > > > > When the new hardware arrives, (about a week), I will probably run some > > tests with varying stripe-sizes and see what happens but any pointers > > towards likely good starting points...... > > There's a fair discussion of stripe sizes in vinum(4), about 200 lines > long, under the heading "Performance considerations". I can't do > better than that in less space. What part of that don't you > understand? > yes, that was a poorly phrased question..... more of a bleat than a question really. What confuses me in particular, is that despite vinum (8) saying that "with modern disk sizes and correct raid implementations there is no reason why stripe sizes of between 2-4mb could not be used" and "a good value for stripe size is betwween 256 and 512 but avoid powers of 2..." The samples then shown in vinum (8) all then use stripe sizes of 512k (a power of 2) or 32k or 64k (distinctly less than 256). This is also common in the cases where I have found sample configurations on the internet. So I am, as we speak, running some tests with various stripe sizes and newfs options to help me see the performance differences for myself. Apologies for wasting your time, I have posted a note on my monitor....."think before you hit the send button" I will also have a look at ccd and atacontrol. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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