On Wed, Mar 24, 2010 at 20:55:07 +0000 (+0000), Daniel Pope wrote:
> On 24/03/10 19:40, Andy Smith wrote:
> > Database heads with storage mounted remotely off a SAN or NAS is an
> > extremely common setup in the real world.
>
> I find that quite surprising. My understanding was that the syscalls (locking
> and mmap) are not supported well enough enough to offer consistency and
> durability guarantees.
Well a SAN just presents disks as SCSI so you get all the SCSI
goodness including supporting multiple initiators and all the locking
(depending as ever on implementation). One place I worked had this
setup:
Server Server
| |
>-----SAN-----<
| |
Disk array Disk array
The SAN was 3km in length. Servers HA and doing host-based RAID-1 to
both disk arrays. You could get the arrays to replicate but that has
several drawbacks (namely another thing to go wrong) and wasn't done.
On the NAS side, it depends whether you are talking about a £0.5M
Netapp box or a £100 bit of kit from PC World as to how well it
supports NFS locking :-)
Adrian
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