Re: [Aoetools-discuss] write buffering and the AoE kernel module
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From: Jon N. <jne...@ja...> - 2007-04-25 22:31:18
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On Wed, 25 Apr 2007, Ed L. Cashin wrote: > On Tue, Apr 24, 2007 at 12:10:02PM -0500, Jon Nelson wrote: > > > > I have several questions about eA.B devices managed by the aoe kernel > > module on Linux 2.6, all centered around write buffering (if any > > exists). > > > > 1. if I open the device with O_SYNC, what (if any) write buffering takes > > place? > > The open(2) manpage mentions that flag, saying that ... Thanks for the answer! However, it doesn't /quite/ answer my question. I should have been clearer. I know all about O_SYNC (although your description is probably the most concise I've ever seen!). What I want to know is what (if any) caveats AoE introduces. Does the aoe driver itself buffer anything before constructing a packet and sending it off? Let me rephrase: Does the AoE driver attempt any sort of write buffering or does the write system call translate directly into packets sent and received? If so, then I think I've got my answer. > > 3. how do things change if I am using a software raid device (such a > > single-device raid1)? > > > > 4. same goes for LVM, etc... > > Those block devices just pass block I/O through to the lower level > block device driver, so they don't really affect the situation. What I'm wondering, then, is why creating a single-disk raid1 (for example) changes the payload sizes of the packets going over the wire, such as when using dd to access the device directly. -- Jon Nelson <jne...@ja...> |