On Wed, 10 Sep 2014 23:24:11 +0200 Bostjan Skufca <bostjan@xxxxxx> wrote: > Hi, > > I have a simple question: > - Where is the code that is used for actual RAID 10 creation? In > kernel or in mdadm? Depends on exactly what you mean ... probably in mdadm. > > > Explanation: > > I was dissatisfied with single-threaded RAID 1 sequential read > performance (basically boils down to the speed of one disk). I figured > that instead of using level 1 I could create RAID level 10 and use two > equally-sized partitions on each drive (instead of one). > > It turns out that if array is created properly, it is capable of > sequential reads at almost 2x single device speed, as expected (on > SSD!) and what would anyone expect from ordinary RAID 1. > > What does "properly" actually mean? > I was doing some benchmarks with various raid configurations and > figured out that the order of devices submitted to creation command is > significant. It also makes raid10 created in such mode reliable or > unreliable to a device failure (not partition failure, device failure, > which means that two raid underlying devices fail at once). I don't think you've really explained what "properly" means. How exactly do you get better throughput? If you want double-speed single-thread throughput on 2 devices, then create a 2-device RAID10 with "--layout=f2". > > Sum: > - if such array is created properly, it has redundancy in place and > performs as expected > - if not, it performs as raid1 and fails with one physical disk failure > > I am trying to find the code responsible for creation of RAID 10 in > order to try and make it more inteligent about where to place RAID 10 > parts if it gets a list of devices to use, and some of those devices > are on the same physical disks. mdadm uses the devices in the order that you list them. > > Thanks for hints, > b. > NeilBrown > > > PS: More details about testing is available here, but be warned, it is > still a bit hectic to read: > http://blog.a2o.si/2014/09/07/linux-software-raid-why-you-should-always-use-raid-10-instead-of-raid-1/ > -- > 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
Attachment:
signature.asc
Description: PGP signature
