[DRBD-user] Mysql on DRBD: Cache Problem?

Lee Christie Lee at titaninternet.co.uk
Fri Aug 1 16:51:16 CEST 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Hi Mark
we're talking about drive cache here, not raid adapter cache.
on SCSI/SATA drives the cache is typically a jumper or a firmware setting that has to be changed via a manufacturer utility. On the later SAS drives it is software controllable through your raid adapter provided that your vendor has implemented the functionality.
By default raid adapters have writethrough cache ON and writeback cache OFF - unless you have a battery backup unit in which case the default will be writeback ON.
After the defaults anything is possible. The cards we use are set to use writeback with BBU, but if a drive fails the card switches to writethrough for additional security.


	From: Mark Eisenblaetter [mailto:mark.eisenblaetter at gmail.com] 
	Sent: 01 August 2008 15:27
	To: Lee Christie
	Cc: drbd-user at lists.linbit.com
	Subject: Re: [DRBD-user] Mysql on DRBD: Cache Problem?
	Hi Lee,
	it seems taht my P400i has no drivewritecache option.
	Wenn i try to modify it comes up whit an error. And in one document i fount that it's default of in P800 controllers,
	so i hope in my p400i too.
	On Fri, Aug 1, 2008 at 3:33 PM, Lee Christie <Lee at titaninternet.co.uk> wrote:

		Most hard drives ship with write-cache enabled.
		When using decent raid controllers its best to turn off the write(back) cache on hard drives. In our testing it makes no difference anyway with a good card.
		Its possible your lost data was in hard drive cache.


			From: drbd-user-bounces at lists.linbit.com [mailto:drbd-user-bounces at lists.linbit.com] On Behalf Of Mark Eisenblaetter
			Sent: 01 August 2008 14:22
			To: drbd-user at lists.linbit.com
			Subject: [DRBD-user] Mysql on DRBD: Cache Problem?
			Hi List,
			I'm trying to run a DRBDMySQL Cluster (Active/Passive) with Replication for easier backup.
			My problem ist that after a hardkill from the master(Powerkill) the slave misses binlog positions.
			After disable the Arraycontroller Write cache its reduced from 100k to 16k Position but that not enough.
			I run DRBD with Protocal C and the minimal max-buffer of 32k.
			Is there any cache i miss? Or somthing else?
			setup: 2x HP DL360G5 whit raid 10 and Gigabit network for drbdsync only.  
			Mark Eisenblätter
			Geissendoerfer & Leschinsky GmbH



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	Mark Eisenblätter
	Geissendoerfer & Leschinsky GmbH

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