[squid-users] multiple cache_dirs: sizing and placement questions

Hello,

Last night I added 2 more cache_dir's because of excessive "Disk overload"
messages and multiple separate (not striped or otherwise RAIDed) spindles
always seems to get recommended. The cache_dirs are on their own
separate/dedicated disks but two disks (the 7.2GB and 3.6GB) are in the same
external diskpack (PCI ultra scsi attached) while the 3rd cache is on a
partition in the 2nd internal disk. It's not the O/S boot disk but it does
share the same internal SCSI controller as the CDROM and boot disk. I am
not actively mirroring - instead I am using Sun's Disksuite to mirror at
night. Once the mirrors are sync'd I rebreak them so that the boot disk is
a "mirror" (d0) but with only one sub-mirror, d10. So during the day no
writes are going to the 2nd disk for the OS, only for the /cache3 dir. My
main concern is does having multiple cache's sharing controllers lose the
gain I sought in adding extra separate disks in the first place? Or is the
loss minimal enough that the advantage of having the multiple disks is worth
it?

Secondly, from the FAQ (
http://www.squid-cache.org/Doc/FAQ/FAQ-8.html#ss8.11 ), I extrapolated the
formula below (I think I posted it before) and then used it to determine how
high the total cumulative cache_dirGB should/could be, per their FAQ.
Hopefully my assumptions/math interpretations are correct and so I guess I
am just asking for a sanity check (did I misunderstand the FAQ or miss
something):

The FAQ says (10MB * cache_dirGB ) + cache_mem + 20MB ) * 2 (twice the
() for physical RAM) = total RAM
That FAQ formula becomes:
Insert known values: ((10 * xGB ) + 256MB +
20MB ) * 2 = 1024MB
Sum cache_mem + extra 20MB : (10x
+ 276 ) * 2 = 1024
divide both sides by 2 to remove "*2":
10x + 276 = 512
subtract 276 from both sides :
10x = 236
divide both sides by 10 :
x = 23.6 GB

With the two extra cache_dirs I now have in total: 7.26GB + 3.6GB + 6.8GB =
18GB
So it *seems* to me that 18GB is well under the 23.6GB limit calculated
above so we should be fine though the FAQ does warn that 64bit systems do
take more RAM (our Squid 2.5STABLE2 is 32bit but the Solaris 8 OS is 64bit).
So if I have made an egregious error, please let me know!

thanks,

Adam
Received on Thu May 22 2003 - 12:56:38 MDT