On Mon, 2004-04-05 at 11:58, Jason C. Leach wrote: > Matt Gulick wrote: > > >On Mon, 2004-04-05 at 10:51, Jason C. Leach wrote: > > > > > >>hi, > >> > >>I have a Promise SX6000 in a RAID5 using Linux Debian on an AMD > >>AthelonXP 2500+. This array will store mostly GIS data. So about 30% > >>large files (a few hundred megs) and 70% small files (several megs). I > >>am curious what stripe block size to use 4-64k (the fs is reiserfs). I > >>was thinking 32k for the stripe block size. > >> > >>Thanks, > >>J. > >> > >> > > > >J, > > > >If the large files are Audio/Video for streaming, then you will want a > >larger stripe size. If not, go with the smallest that you can (a small > >~.h or text file will take the same amount of space as your stripe > >size). > > > >The best way to set this is to consider the total volume size. What > >will be the allocation block size be for that size of volume if it were > >on a single disk for that OS?. Set you allocation size to be the same > >or some multiple of that value. > > > > > > > Thanks for the reply. The total volume size will be 800G. I'm not sure > what reiserfs/Linux would use for the block size if that were on one > disk. Can you give me some tips? > > A significant portion of the files will be a few megs and above, not > really any .h or other small text files (say 1%). No streaming > audio/vid. The GIS data will be csv files, shape files, large TIF > files. Is it better to go smaller then larger with the stripe block size? > J. The stripe size really is dependent on the usage. For streaming content, large stripes result in fewer head seeks which take a relatively large amount of time and can impact throughput. For use with data base type access, a stripe size equal to the record size would be best. For what you describe, I would use a stripe size that is no more than 1-2 X the allocation block size. An example of a bad stripe size: Stripe Size = 64K Allocation Size = 48k Each Stripe read will read 2 or more allocation blocks and have to extract the correct data. This gets real messy when allocation blocks require more than a single read. Writes are even worse because now you need to do a read-modify-write for each block access unless the data is in a cached block. Even then, the fs still has to buffer move the data into the cached block before writing the data. The same is also true where the Strip is smaller than the allocation blocks. What I would do is create the stripe using the smallest stripe allowed by whatever tool you use. Create a directory or two and save a small (2-3 text bytes with gedit or vi will do) file. Do an ls -al on the volume and look at what the size of the directories and the text file are. This will be a good indication of the allocation size. Now, reformat the RAID with that as your smallest stripe size. You can make the stripes larger if you want, but always make them an integral multiple of the allocation size. Good luck. Matt ---------------------------------------- Matt Gulick Sr. Staff Engineer Adaptec, Inc. gulickconsulting@direcway.com matt_gulick@adaptec.com (715) 426-0884 - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
