Hi I'am writing an application that write a stream of pictures of fixed size on a disk. My app run on a self integrated gnu/linux (based on a 2.6.31.6-rt19 kernel). My media is formated with # mke2fs -t ext4 -L DATA -O large_file,^has_journal,extent -v /dev/sda3 [...] And it is mounted with # mount -t ext4 /dev/sda3 /var/data/ EXT4-fs (sda3): no journal EXT4-fs (sda3): delayed allocation enabled EXT4-fs: file extents enabled EXT4-fs: mballoc enabled EXT4-fs (sda3): mounted filesystem without journal My app opens the file with "O_WRONLY | O_CREAT | O_TRUNC | O_SYNC | O_DIRECT" flags. Each write takes ~4.2ms for 304K (it is very good since it is the write bandwidth of my hard drive). There is a write every 100ms. But every exactly 646345728 bytes, the write takes ~46ms. I had the same problem with ext2 but every ~620M (the amount wasn't so constant). Also i tryed to "posix_fallocate" with (eg 2G), and the first write overhead comes at this limit. I would like to avoid to preallocate. I suppose it is a kind of block allocation issue. But i would like to have your opinion : - what is exatcly this amount of bytes ? - can i do something for having a "constant" write time from the user space point of view ? - is it a "probem" only for me ? Thank you for your reading. Paul. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
