I have an existing RAID Array and I want to increase the readahead setting. But the device has already been formatted and contains data that I cannot afford to lose. I'm unfamiliar with the blockdev command. Is it safe to run blockdev --setra=xxxxx on devices that have already been formatted? Will running the following command destroy (delete) the data on my device? Is there any risk of this happening?
$ blockdev --setra 65536 /dev/md0
Not sure this is important, but here are the devices details:
$ xfs_info /data/d1 meta-data=/dev/md0 isize=256 agcount=16, agsize=8191936 blks = sectsz=512 attr=2 data = bsize=4096 blocks=131070976, imaxpct=25 = sunit=64 swidth=256 blks naming =version 2 bsize=4096 ascii-ci=0 log =internal bsize=4096 blocks=64000, version=2 = sectsz=512 sunit=64 blks, lazy-count=1 realtime =none extsz=4096 blocks=0, rtextents=0 $ sudo mdadm --detail /dev/md0 /dev/md0: Version : 1.2 Creation Time : Thu May 5 17:23:35 2011 Raid Level : raid0 Array Size : 524283904 (500.00 GiB 536.87 GB) Raid Devices : 4 Total Devices : 4 Persistence : Superblock is persistent Update Time : Thu May 5 17:23:35 2011 State : clean Active Devices : 4 Working Devices : 4 Failed Devices : 0 Spare Devices : 0 Chunk Size : 256K Name : d1:0 UUID : 16d7fee4:a8903d2f:28c65d2f:161006b5 Events : 0 Number Major Minor RaidDevice State 0 202 241 0 active sync /dev/sdp1 1 202 242 1 active sync /dev/sdp2 2 202 243 2 active sync /dev/sdp3 3 202 244 3 active sync /dev/sdp4