Server vs. server
09 01 10 - 21:46
Some people like strong cars, I like powerful computers. Since I got on the internet in 1994 or so, this reads powerful servers. My last workstation oriented powerful computer was Pentium 200 in 1996 and it soon landed in the role of a server, with 4x 25GB drives in 1999. Btw, it still works perfectly ;)
Since home server is mostly limited by budget, one looks at price/performance factor. And since I have all the storage management (raid/lvm) expirience, I spent some time putting together a data-reliable machine, that serves the usual music/movies entertainment stuf, runs a samba share for few windoze boxen to share their data and a few NFS and AoE exports for my desktop. Since my desktop is diskless (actualy has no moving parts), it is very dependant on latency and io throughput the server offers it.
For a few years now this role was handled by a HP tc2120 "server" I got cheaply second-hand. Pentium 4, 64bit pci bus, looks like a decent IO oriented pc. I hang a pair of ide disks on onboard ide, a few more on addon ide cards and a bunch of sata disks on LSI 1068. All disks were in mirrored pairs (same size, different manufacturer) and joined together in one volume group. Out of that I carved various logical volumes for various tasks. One such volume was used for torrent downloads.
And how was I satisfied with it? It was barely useful. Every time software mirrors were doing a resync, latencies grow beyond anything I would consider useable. Every time a torrent was active, the whole system lagged. IO to one volume killed IO on others. I tried many things, like decreasing raid resync speed (helped only a little and slowed down resync time to a week or so), changing schedulers (no observable change), readahead settings (marginally better on read-mostly nfs mounts). At the end I concluded that it must be the interactions of all the storage layers that create artificial relations among diffrerent disks that are standing in my way and greatly decreasing the overall system performance.
Because I'm moving soon to a different house, I decided on setting up a less powerful server here and taking this "nice" HP box with me, configured differently, of course. I dug up an old slot1 Pentium 3 pc, put desktop gigabit nic and 3ware 6800 in it and stuffed it with disks. There's only one mirror now and 3ware takes care of it, all other disks are jbod, standalone, no lvm. Each disk has its own scheduler and readahead settings that depend on how it is used. Expirience: same throughput as HP "server", much better latencies, much better paralelism. Suprisingly this 12 years old pc is capable of sustained 50MB/s over ethernet to different disks, a number that I've only seen in bursts on HP "server". Oh, and it also draws about half as much power as Pentium 4. And it serves you this page you're reading now.
So much about "new and improved" technology. Complex setups are rarely better than simple setups. Cheap, fast, reliable: pick any two, you can't have all three. What more can I say? ;)
