Date: Fri, 13 Dec 2002 14:02:05 -0800 From: Tim Kientzle <kientzle@acm.org> To: stable@FreeBSD.org, marius@malkav.snowmoon.com Subject: Re: memory disks in 4.5-stable Message-ID: <3DFA58DD.50001@acm.org>
next in thread | raw e-mail | index | archive | help
> I want to create a number of small RAM disks on some webservers so they > can serve high traffic content directly off of RAMdisks instead of > conventional disks or NFS. I would strongly suggest you do some load-testing before you do this on a production machine. Otherwise, you might waste a lot of time on something that gives you no performance benefit at all. (In fact, naive use of RAM disks can significantly impair overall performance.) Make sure that your test machine is as close as possible to your production configuration: same RAM, same disk, same CPU, same NIC. (If your production environment uses NFS, use NFS in your test environment.) Copying data to a RAM disk is just an attempt to manually cache data in RAM. Generally speaking, the kernel is pretty smart about deciding what is best to keep in RAM. It will use spare memory as disk cache. (If it has spare memory; just adding memory might help.) If the bulk of your traffic is a few tens of MB of data from a local disk, that data will generally end up being kept in RAM anyway; a RAM disk won't help. NFS is a slightly different story, though. Because of the nature of NFS, the kernel is not allowed to be as aggressive about caching data in RAM. Copying NFS content to a local hard disk can be a big speedup because the kernel can then do more aggressive disk caching. (Although, sometimes it works the other way around; a cheap local disk can actually be slower than a well-tuned RAID array accessed over 100Mbps or 1Gbps Ethernet.) Like I said, you should test very carefully before using this approach in production. Tim Kientzle To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-stable" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?3DFA58DD.50001>