02-25-2019
It all comes down to the homonyms cash & cache.
How much is you budget for cache? That's the key really. SSD is slightly slower than cache.
For write operations, you would have to balance off the time to commit the update to real disk (even if it is SSD) between the two. if you pass the update to a SAN, it will respond very quickly to say that you have written it, but it will actually write the data in its own time. The update is cached for write but you can continue. There will be cache batteries for power loss before it's really written. For local disk, it depends. Does the RAID controller have a good cache allocation and would therefore behave in the same way? If not, you (the operating system) must ensure that the write is complete before you proceed (costing CPU Sys time I think) and that can confusingly make local IO slower.
You have, of course, stated that this is a read intensive server so your other thing to consider is cache/RAM in the server. The server will fill up with the data you read in normally anyway, but if you wish, you could pre-read the data to give it a head-start. Beware that you need to have lots of memory for this else you will just drop it again. You can just do a find for the files of data you want and cat them to /dev/null so that they get read. Is 512Gb sufficient for your data? You don't say how much you have.
I hoe that my thoughts help,
Robin
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CFS(4) Kernel Interfaces Manual CFS(4)
NAME
cfs - cache file system
SYNOPSIS
cfs -s [-rd] [-f partition]
cfs -a netaddr [-rd] [-f partition] [mtpt]
DESCRIPTION
Cfs is a user-level file server that caches information about remote files onto a local disk. It is normally started by the kernel at boot
time, though users may start it manually. Cfs is interposed between the kernel and a network connection to a remote file server to improve
the efficiency of access across slow network connections such as modem lines. On each open of a file cfs checks the consistency of cached
information and discards any old information for that file.
Cfs mounts onto mtpt (default /) after connecting to the file server.
The options are:
s the connection to the remote file server is on file descriptors 0 and 1.
a netaddr
dial the destination netaddr to connect to a remote file server.
r reformat the cache disk partition.
d turn on debugging
f partition
use file partition as the cache disk partition.
All 9P messages except read, clone, and walk (see intro(5)) are passed through cfs unchanged to the remote server. A clone followed imme-
diately by a walk is converted into a clwalk. If possible, a read is satisfied by cached data. Otherwise, the file server is queried for
any missing data.
FILES
/dev/hd0cache
Default file used for storing cached data.
SOURCE
/sys/src/cmd/cfs
CFS(4)