Messages in this thread | | | Date | Sat, 15 Mar 2008 16:40:22 -0400 | From | "Mike Snitzer" <> | Subject | Re: [ANNOUNCE] Ramback: faster than a speeding bullet |
| |
On Sat, Mar 15, 2008 at 4:26 PM, Pavel Machek <pavel@ucw.cz> wrote: > On Thu 2008-03-13 12:03:03, Daniel Phillips wrote: > > On Thursday 13 March 2008 12:50, David Newall wrote: > > > Daniel Phillips wrote: > > > > The period where you cannot access the data is downtime. If your script > > > > just does a cp from a disk array to the ram device you cannot just read > > > > from the backing store in that period because you will need to fail over > > > > to the ramdisk at some point, and you cannot just read from the ramdisk > > > > because it is not populated yet. > > > > > > Wouldn't a raid-1 set comprising disk + ramdisk do that with no downtime? > > > > In raid1, write completion has to wait for write completion on all > > mirror members, so writes run at disk speed. Reads run at ramdisk > > speed, so your proposal sounds useful, but ramback aims for high > > write performance as well. > > raid1 + kflushd tweak? > > special raid1 mode that signals completion when it hits _one_ of the > drives, and does sync when the slower drive is idle?
raid1 already supports marking member(s) as write-mostly. Any write-mostly member can also make use of write-behind mode (provided you have a write intent bitmap).
| |