about ssd/hdd ssd is better for unaligned reads/writes (.1ms access time) the problem is... we don't have a 'math model' to simulate and select the best disk to send read it's a bit difficult, and maybe we won't have one since we have many kind of devices (nbd, ssd, hd, ssd+hd, sd cards, etc) i think the only good improvement is allow better unaligned read to ssd, and aligned reads to hdd i tested some benchmarks ago and a better tunned read balance algorithm can only allow 1% less time to stop benchmark (speed) maybe flashcache and bcache can give more 'speed' i didn't tested 2011/7/29 Doug Ledford <dledford@xxxxxxxxxx>: > On 07/29/2011 10:55 AM, David Brown wrote: >> >> One thing has occurred to me while reading this thread - it seems to be >> an assumption here that SSD's are faster than HD's. In one area - access >> times - SSD's are very much faster. But when transferring bulk data, >> they are not necessarily faster. > > Not necessarily, no. But, if you do like I did and pick your SSD carefully, > they are. I specifically chose the one I did because it was SATA-III with a > 6MB/s link speed and it was rated for 400+MByte/s reads and 210MByte/s > writes. Here's the link: > > http://www.newegg.com/Product/Product.aspx?Item=N82E16820233154 > > There are even faster ones out there now. > > But, I was worried about the drive wearing out under the frequent checkouts, > builds, etc. so hence the reason I have two hard drives backing it up. When > it does wear out, I'll put a new one in, add it to the array, wait for > resync, all done. > >> Certainly a pair of good hard disks in >> RAID10,far will stream reads and writes with a similar throughput to >> many SSD's. An ideal situation is therefore that small reads will come >> from the SSD, but that bulk reads could come from any disk that is >> currently idle. Enabling "write-behind" on the hard disks would still be >> a big gain on the write latency. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Roberto Spadim Spadim Technology / SPAEmpresarial -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
