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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HOME(8) System Manager's Manual HOME(8)
NAME
home, 40meg, 80meg, personalize, update, Disclabel - administration for local file systems
SYNOPSIS
gnot/home
gnot/personalize
gnot/update
magnum/home
magnum/personalize
magnum/update
pc/40meg
pc/80meg
pc/personalize
pc/update
nextstation/home
nextstation/update
DESCRIPTION
These programs help maintain a file system on a local disk for a private machine.
Home partitions a disk, copies the appropriate kernel to the disk, and makes a new file system on the disk. To do this, it overwrites the
vendor-supplied software on the disk with a copy of Plan 9. 40meg, 80meg, and 100meg configure disks and make file systems for disks of
the appropriate size.
Update copies the current kernel to the disk and updates files on the local file system. It only updates those files put there by the home
program.
Personalize removes the contents of the /usr directory on the local disk and copies a minimal set of files for the user who runs the com-
mand.
The file /rc/bin/nextstation/Disclabel, despite its name, is not an rc(1) script. It contains the second stage bootstrap program for
Nextstations booting from local disk. Before booting a Plan 9 Nextstation from disk, it should be installed in the partition
/dev/hd1label; this is normally done by nexstation/home.
FILES
/lib/proto/portproto
Mkfs prototype files for magnum/home, magnum/update, gnot/home, and gnot/update.
/lib/proto/386proto
Mkfs prototype files for pc/40meg, pc/80meg, and pc/update.
SOURCE
/rc/bin/gnot/*
/rc/bin/magnum/*
/rc/bin/pc/*
/rc/bin/nextstation/*
SEE ALSO
kfs(4), mkfs(8), prep(8), wren(3)
``Installing the Plan 9 Distribution''.
HOME(8)