Several people have reported issues with combining OS and OSD journals on the same SSD drives/RAID due to contention. If you do something like this I would definitely test to make sure it meets your expectations. Ceph logs are going to compose the majority of the writes to the OS storage devices. On Mon, Nov 25, 2013 at 12:46 PM, James Harper <james.harper@xxxxxxxxxxxxxxxx> wrote: >> >> We need to install the OS on the 3TB harddisks that come with our Dell >> servers. (After many attempts, I've discovered that Dell servers won't allow >> attaching an external harddisk via the PCIe slot. (I've tried everything). ) >> >> But, must I therefore sacrifice two hard disks (RAID-1) for the OS? I don't see >> why I can't just create a small partition (~30GB) on all 6 of my hard disks, do a >> software-based RAID 1 on it, and be done. >> >> I know that software based RAID-5 seems computationally expensive, but >> shouldn't RAID 1 be fast and computationally inexpensive for a computer >> built over the last 4 years? I wouldn't think that a CEPH systems (with lots of >> VMs but little data changes) would even do much writing to the OS >> partition....but I'm not sure. (And in the past, I have noticed that RAID5 >> systems did suck up a lot of CPU and caused lots of waits, unlike what the >> blogs implied. But I'm thinking that a RAID 1 takes little CPU and the OS does >> little writing to disk; it's mostly reads, which should hit the RAM.) >> >> Does anyone see any holes in the above idea? Any gut instincts? (I would try >> it, but it's hard to tell how well the system would really behave under "real" >> load conditions without some degree of experience and/or strong >> theoretical knowledge.) > > Is the OS doing anything apart from ceph? Would booting a ramdisk-only system from USB or compact flash work? > > If the OS doesn't produce a lot of writes then having it on the main disk should work okay. I've done it exactly as you describe before. > > James > > _______________________________________________ > ceph-users mailing list > ceph-users@xxxxxxxxxxxxxx > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com -- Kyle _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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