[lug] Robust storage
stimits at comcast.net
Tue May 3 13:26:32 MDT 2005
>>I've had extremely good luck with Linux software RAID over the same time
>>period. Oh, add to it that the software RAID is well documented, if in no
>>other way than through the code. A local guy lost his 3ware RAID array in
>>his home box last summer, it just got confused and he couldn't recover it.
>>He basically had the data, but needed to tell the controller, through
>>poking appropriate bits onto a new drive, to bring the array back up, but
>>3ware wouldn't cooperate with documenting those parts of the drive.
> Which flavor of disks are you using with Linux software RAID? Any
> special hdparms you pass?
IMHO, if you want reliable disks, get SCSI. I like the modern Seagates.
In all cases, keep the drive cooled, don't ever stack 2 drives next to
each other without some sort of fan or metal cooling frame (most hot
swap bays do this if they are not plastic frames). No hdparms needed.
>>Really, the battery backed up cache on the controller is for performance,
>>not safety. It allows the controller to confirm data written to the disc
>>when it gets into the cache, instead of the normal case where it waits for
>>it to get on the disc. The problem here is the added complexity may lead
>>to other subtle problems, as we saw with livejournal.
> The write cache is most definitely for performance. However, the
> battery backup is for safety in case of power loss prior to the cache
> being written to disk. In the case of livejournal, they had write
> cache enabled on both the RAID card and the drives - I can't recall a
> situation in which everyone lying to each other was a good thing. ;-)
Don't know if it actually works, but several disks will use the energy
of the spinning disk to power a buffer flush if power dies, even without
battery backup. I have no idea which disks try this, but it was
fascinating reading about it a couple of years ago. Anyone know if this
technology actually works or which disks try it?
D. Stimits, stimits AT comcast DOT net
More information about the LUG