2) executing the "mdadm --create ..." command using different options (see bellow for list) than have been used when array have been created originally:-> different chunk size -> different layout -> different disks order 3) resync-ing the array it is for the OS, which probably contain a lot of small files. It includes 128 KB for the RAID superblock. Increasing the stripe width adds more disks and can improve read/write performance if the stripe width (chunk size) is greater than the data size. (As a side-note, please take into account that the mdadm manual page, as of the date of writing this part, states that the default chunk size is 512 KiB.) It will print the superblock and lists the chunk size there. If using ext3/4, be sure to calculate your stripe-width when you format the FS. • When growing a raid0 device, the new component disk size (or external backup size) should be larger than LCM(old, new) * chunk-size * 2, where LCM() is the least common multiple of the old and new count of component disks, and "* 2" comes from the fact that mdadm refuses to use more than half of a spare device for backup space. The parameters talk for themselves. Replace SIZE with an integer value in kilobytes for the desired size. mdadm's current default is 512 KiB. EDIT: See here and here on chunk size in RAID1 Note that the switch is -E, not -e. See the third grey section here. It can be found with mdadm: # mdadm --detail /dev/mdX | grep 'Chunk Size' No need with xfs.-- Dave Mdadm (pronounced "m-d-adam") is a tool for Linux for managing software RAID devices in Linux. 1. which is the best chunk size and best configuration for raid 0? The chunk size is a property of the RAID array, decided at the time of its creation. In order to get the best array performance, you need to know the correct chunk size and the golden rule for choosing it: small inputs / outputs = large chunk, and large inputs / outputs = small chunk. The mdadm tool will start to mirror the drives. mdadm: Note: this array has metadata at the start and may not be suitable as a boot device. For example, the following command sets the segment size for each RAID device to about 40 GB where the chunk size is 64 KB. You … mdadm --create --verbose /dev/md0 --level=linear --raid-devices=2 /dev/sdb6 /dev/sdc5 should create the array. mdadm -E /dev/sda1 or similar against one of the devices in the array. There used to be a lot of hand tuning with nested raid configs, chunk-size, etc, but these days you can pretty much just throw a --level=5 at it and be fine. 2. which is the best chunk size for raid 5, which will contain a lot of big files (1-2gb)? It would be different if you had 20+devices, but for 3 devices, you're probably fine. If you plan to store '/boot' on this device please ensure that your boot-loader understands md/v1.x metadata, or use --metadata=0.90 mdadm: size set to 104792064K Continue creating array? For example: Chunks: the hidden key to RAID performance (from 2007), which suggests quite small chunks by today's standard; Cache Cache is simply RAM, or memory, placed in the data path in front of a disk or disk array. The RAID chunk size refers to those parts of the strip into which it is divided. M. These are derived from the RAID chunk size, the filesystem block size, and the number of "data disks". (A kilobyte is 1024 bytes.) The output might look like this mdadm: chunk size defaults to 64K mdadm: array /dev/md0 started. y. thanks a lot. Chunk size; Let's look at all three. 64k is default in mdadm. Have a look in /proc/mdstat. With an integer value in kilobytes for the OS, which will contain a lot of big (... 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