Hello Neil, Thanks for the reply. I was working on the internet scsi(iscsi drivers provided by intel) and software raid configuration for my thesis in Storage Area Network. The problems right now i am facing is 1> For a local disk write for 512 mb in DELL 1.2 Ghz it takes me 1 min. 2> For a single iscsi device write, the transfer of data takes place at 4000 bytes/sec. 2> For raid configuration, the rate is pretty slow ( 40 bytes/sec). One thing i have observe is that write to one of the device( from a total of 2 device) takes for few minutes and then stop. I was trying to figure what routines in the operating system code, I might need to look into to understand a problem if there is one. Some more problems. If one of the network comes down, the mkfs for the raid , hangs. >A raid0 array can be made of a number of drives of differing sizes. >To accomodate this we divide the address space into several blocks. >The first block is striped across all drives to the size of the >smallest. The next block is striped across the remaining drives to >the size of the next smallest, etc. Is there a relation between chunk size and block size of raid. Is this similar to buffer size( write(fd,&buffer,buffer_size) and block size of filesystem. -Jay >===== Original Message From Neil Brown <neilb@cse.unsw.edu.au> ===== >On Sunday October 12, jshankar@CS.ColoState.EDU wrote: >> Hello, >> >> >> I was testing the raid0 configuration for the iscsi device ( /dev/sdb and >> /dev/sdc). >> >> For writing a 512MB in a LAN environment it was taking 24 hrs. i was going >> through the source code of raid0.c and certain things doesn't made sense to me. >> >> 1> what role does the Hash bit play. > >A raid0 array can be made of a number of drives of differing sizes. >To accomodate this we divide the address space into several blocks. >The first block is striped across all drives to the size of the >smallest. The next block is striped across the remaining drives to >the size of the next smallest, etc. > >Mapping from a virtual device address to block and thence a drive and >offset is not straight forward. It requires a table search. The hash >table helps accelerate this search. > > >> 2>If my chunk size is 8 byte. Does that mean it will write 8 byte into device 0 >> and then into device 1. Is the write request to the disk in synchronous or >> asynchronous mode. >> >You cannot have an 8byte chunk size. 4K is the minimum. >With an 8K chunk size and 2 devices, > sectors between 0 and 8K, 16k and 24K, 32K and 40K, 48K and 56K etc > are written to the first device. > sectors between 8K and 16K, 28K and 32K, 40K and 48K etc > are written to the second device. > >raid0 does not impose any synchronisation. Writes are only >synchronous if the filesystem waits for them. raid0 never waits. > >> >> 3> Is wite_disk_sb in md.c responsible for writing into disk??. Is fsync_dev >> responsible for synhronous write ??. If so can i change to asynchronous write.I >> will really appreciate if somebody can tell me what all routines I need to go >> through to figure out the functionality of raid0 behaviour. > >write_disk_sb is for writing the raid superblock to disk. It doesn't >happen often. >fsync_dev is fairly irrelevant. You can safely ignore it. > >I hope that helps. > >NeilBrown > >> >> Thanks >> Jayshankar >> >> - >> To unsubscribe from this list: send the line "unsubscribe linux-raid" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
