[DRBD-user] I/O barrier problem

Petrakis, Peter Peter.Petrakis at stratus.com
Mon Nov 3 16:31:04 CET 2008

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

Hello Hervé,

The cciss driver doesn't support i/o barriers, however, if you have a BBWC
(battery backed write cache) you should be fine. I recently explored the
possibility of adding barriers though the available specs don't confirm
whether SYNCHRONIZE CACHE is supported, they do however support the ability
to flush the entire cache, which would kill performance. I've been in contact with HP in search of a definitive answer and what I got was "there's a new spec coming out" and they don't know when it'll be ready.

I agree that there ought to be a way to flush the cache to the physical disks associated with a single logical volume but until there's a definitive answer, any i/o barrier implementation would essentially be unpredictable.
Feel free to ask HP regarding this issue :)


P.S. http://cciss.sourceforge.net

> -----Original Message-----
> From: drbd-user-bounces at linbit.com [mailto:drbd-user-bounces at linbit.com]
> On Behalf Of GAUTIER Hervé
> Sent: Monday, November 03, 2008 8:12 AM
> To: drbd-user at linbit.com
> Subject: [DRBD-user] I/O barrier problem
> Hi there !
> I need some more explanations in order to know from where comes a
> barrier problem (message local disk flush failed with status -95).
> I have identified the following different levels of the chain that may
> be involved:
> - OS: I am currently running on Red Hat Enterprise Linux ES release 4
> (Nahant Update 6) kernel 2.6.9-67.ELsmp. Is there a minimum required
> kernel version for the barriers implementation ?
> - DRBD: The current version I am using is drbd-8.2.5.
> - Drivers: I currently use disks connected on a HP Smart Array 642
> Controller using the cciss driver 2.6.16 provided by the Red Hat
> Enterprise Linux ES release 4 (Nahant Update 6). I haven't seen any
> option on this driver.
> - Controller: I will check in there is any cache option in the HP Smart
> Array 642 Controller firmware.
> - Disks: I will try to find any information on the disks used in order
> to check if the used some cache.
> Anything else I have forgotten ?
> Thank in advance,
> Best regards.
> --
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