On 7/18/06, Jon Nelson
On Tue, 18 Jul 2006, Dave Howorth wrote:
HG wrote:
Hi!
I'm planning to build a home made NAS using old harware and SUSE. SUSE might not be the best OS for this, but it's the only Linux I have administered at least somewhat.
Ok, what I'm thinking is a old PC with lot's of old disks inside and a gigabit ethernet (planning to do video editing over it also).
Even gigabit ethernet is WAY slower than local disks. You may find it a pain for video editing. It might be OK to store video there, copy it to a local disk while you edit it and then copy it back. But the bottom line is experience - I suggest you set up the gigabit link and run some tests with it first :)
Do you mean to say that gigabit ethernet has less bandwidth than local disks or that the latency of gig-e is higher? Unless you have some pretty beefy local disks, gig-e has rather more bandwidth than most local disks. As for latency, that's not something I can answer, but the track-to-track on most disks these days is something like 8 ms (right?), which my local network easily beats. What is the round-trip-time on something like NFS versus local disks?
I'm not flat-out saying you are wrong, but I'd like you to qualify your statements and help me understand exactly what you are saying.
As an example, in a situation involving fast ethernet (not gig-e) and some mid-grade machines (just shy of 1GHz and basic consumer-grade IDE disks) my local disks top out around 11.45 MB/s (hdparm -t), averaging 8.9 MB/s (dd if=/dev/hda of=/dev/null bs=4k count=10000). Contrast that with a recent test I performed using ATA over Ethernet, where the disks were a raid5 on a similar machine but faster disks (about 20MB/s local read speed on the backing store for the ata-over-ethernet block device) - the exact same client was able to sustain 11MB/s and with less load, and not-very-good ethernet cards. By this quick test, and measuring "bandwidth", ata-over-ethernet was just as fast as, and sometimes faster than, my local disks. (Granted, not the best test components or the best test, but it serves to illustrate.) With gig-e one could easily exceed my local disk speed on a regular basis.
Question: what might be the best way to calculate "latency" in a way that could be used to compare (for example) ATA-Over-Ethernet to a Local Disk (both are block devices to the client).
-- Carpe diem - Seize the day. Carp in denim - There's a fish in my pants!
Jon Nelson
Jon, Your local speeds seem slow (i.e. unoptimized). I spent a lot of time a few years ago doing speed tests and getting good disk controllers in my machines. With those optimized machines I see very good dd speeds with the command dd if=/dev/hde of=/dev/hdg bs=4k conv=noerror,sync IIRC, the speeds I see are generally like: 1 GB/min if the source is a laptop drive 2 - 2.5 GB/min if the source is an standard non ATA-133 drive 3 GB/min with a ATA-133 source/dest 4 GB/min with SATA-150 drives I have not yet tested SATA-300 drives. All of the above are for simple drives, not high-speed raid10 setups. Your 11 MB/sec is only .6GB/min. If you care about performance you need to get that faster, especially in your NAS. One thing I have learned is to not use the MB IDE controller for anything performance related. A $50 PCI controller will be a lot faster. I get one with 2 IDE connectors and only use the Master drive. ie. one drive on each ide cable. Back to the OP's issues: Gig-e should be 50-75% of 100MB/sec = 50-75% of 6GB/min. As you say that should be fast enough to make remote access as fast as local. Not sure about the NFS etc. overhead. Note that in a high-speed data center environment where they are running large RAID 10 arrays, gig-e will not keep up. That is why they spend the money for 4 gb/sec fibre-channel, etc.. Also, if your going to be handling large video files think about using XFS for your data partitions. It was specifically designed to work extremely fast with large files. Greg -- Greg Freemyer The Norcross Group Forensics for the 21st Century -- Check the headers for your unsubscription address For additional commands send e-mail to suse-linux-e-help@suse.com Also check the archives at http://lists.suse.com Please read the FAQs: suse-linux-e-faq@suse.com