atari Posted March 15, 2009 Share Posted March 15, 2009 Hardware: I'm using the hardware that LimeTechnology currently sells in the systems they build - minus the extra pci-e sata2 cards (only using cards onboard C2SEE). Components: Supermicro C2SEE motherboard E5200 CPU Corsair 2GB DDR3 memory 4x Seagate 1.5 TB drives 1x Samsung HD103UJ 1TB drive The Samsung drive hdparam results: # hdparm -tT /dev/sde /dev/sde: Timing cached reads: 2566 MB in 2.00 seconds = 1283.94 MB/sec Timing buffered disk reads: 352 MB in 3.02 seconds = 116.74 MB/sec The Seagates look like this: /dev/sda: Timing cached reads: 2528 MB in 2.00 seconds = 1264.90 MB/sec Timing buffered disk reads: 382 MB in 3.01 seconds = 126.91 MB/sec But when I use mc to copy files between them, I get ~16MB/s according to mc. This seems pretty slow? No write-cache drive set up yet.... but is it really this slow? Quote Link to comment
prostuff1 Posted March 15, 2009 Share Posted March 15, 2009 This is about normal as you have to take into account the parity that is being calculated for each one of those read and writes. There was a good explanation of it somewhere but i am to lazy to find the link… sorry. Quote Link to comment
Biggy2872 Posted March 15, 2009 Share Posted March 15, 2009 This is about normal as you have to take into account the parity that is being calculated for each one of those read and writes. There was a good explanation of it somewhere but i am to lazy to find the link… sorry. I believe you are talking about bjp999's post here: http://lime-technology.com/forum/index.php?topic=3454.msg29810#msg29810 Cheers, Matt Quote Link to comment
atari Posted March 15, 2009 Author Share Posted March 15, 2009 ack. Well... that kind of sucks. I suppose the price to pay for data integrity. I'll hook up a cache drive asap Quote Link to comment
RobJ Posted March 15, 2009 Share Posted March 15, 2009 That 16MB/s sounds amazing, possibly the best I've heard. You have to remember that it is not just that writing to a parity protected drive involves 4 times the drive I/O, but that also the 2 initial reads are followed by 2 writes to the same sectors. That means it has to wait for a complete rotation of the platters after the read, before it can write them. So sequential read times are unfortunately not applicable here. And because it is one long sequential process, the drive cache and OS buffers are not a help here either, as none of their contents are being reused. Really makes you appreciate the Cache drive... Quote Link to comment
SSD Posted March 16, 2009 Share Posted March 16, 2009 ack. Well... that kind of sucks. I suppose the price to pay for data integrity. I'll hook up a cache drive asap Remember that although the write performance is on the slow side, the read performance is not. unRAID is first and foremost a media server. The very nature of media is that it is mostly reading. Quote Link to comment
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