Problem: If you use IDE or SATA Disc Drives inside your Workstation or Server without a additional uninterruppted power supply after a power loss your Disc Drives can lose data, do not boot clean up agian or damage the drive headers and sectors.
Background: SATA or IDE Drives uses „Disc Cached Controllers“, the count of this disc cache reach from 8 to 64 megabytes. In case of data write to disc, the disc controllers do cache some data who are often used. A Raid 1 Disc Mirror is affected too by this problem. SCSI od SAS are not using Cache by default.
Solution:
Install the software tool called hdparm to set the cache parameters to disabled, cause most of operating systems have enabled by default.
- at Debian/ubuntu do : # sudo aptitude install hdparm
- at Centos/Redhat do: #sudo yum install hdparm
now lets show discs which are installed:
- at Debian/ubuntu do: # sudo fdisk -l
- at Centos/Redhat do: #sudo /sbin/sfdisk -l
- at FreeBSD do: # fdisk -l
yet lets take settings to disable the cache on every boot:
- at all linux do: sudo nano /etc/rc.local
- insert for every drive
hdarm -W 0 /dev/sdX
(X is for a to …) - at FreeBSD do : #vi /etc/loader.conf
- insert once for all drives
hw.ata.wc="0"
Remarks:
- If you have two drives with same physical size inside your PC config a mdadm Software Raid 1 additional on your System.
- Set the PC Bios Settings to auto boot ofter power failure and plug off the power on you testing System, check the results. There should not be needed a check disk called fsck after the Test, but its better to do it.
- Hardware Raid Controllers do often have RAM Cache too, size 128MB up to 2GB, at power loss these Data lost, this can only be surpressed by a addtition RAM Cache Backup Battery connected to the Hardware Raid Controller