> Date: Thu, 4 Dec 2008 17:11:46 -0500 > From: "Josh Carroll" <[EMAIL PROTECTED]> > > > It seems that the term "swap-backed" is misleading for some people. It does > > NOT mean your md(4) device will be constantly swapping to disk (and the man > > page does an alright job of relaying this). It simply means that generally > > available memory will be used, and so will swap iff available memory happens > > to drop low enough. > > > > The bottom line in my experience with md(4) devices greater than ~100MB is > > that "swap-backed" is always reliable, while malloc'd md(4) devices will > > cause unpredictable kernel panics. > > Using -t swap instead of -t malloc will prevent a panic, but creating > an md greater than the size of the VM available and filling it will > cause resource exhaustion and OOM will kick in and start killing > processes, right? So while it won't panic the box, I still wouldn't > consider it safe to use unless the size of the md is chosen carefully. > Someone please correct me if I'm wrong, but I think that'd be the > behavior if an md with -t swap is used, right?
Yes, but the VM available is just a bit larger than the amount of KVM. you still need at least a bit of sanity when you create (and fill) an MD device. For performance reasons, I suggest keeping the size of an MD so that it will fit in RAM. Paging in and out is rather painfully slow. -- R. Kevin Oberman, Network Engineer Energy Sciences Network (ESnet) Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab) E-mail: [EMAIL PROTECTED] Phone: +1 510 486-8634 Key fingerprint:059B 2DDF 031C 9BA3 14A4 EADA 927D EBB3 987B 3751
pgp21Z1PUABh1.pgp
Description: PGP signature
