We have had some form of experience in this sceanrio, where we upgraded one
of our squid boxes from 4 x 160 GB SATA II (5400 rpm) to 4 x 250 GB SATA II
(7200 rpm). The speed increase was noticeable. However, as far as I've
read through, the following seems to be the main decision making criteria:
1. Disks used for Cache Store should absolutely not have the OS, logs, swap
partitions (extensive documents on the internet exist).
2. Swapping of memory is also not recommended, with swap partition disabled
(some documents on the internet refer to this).
3. Single disk cache stores are the fastest (though not tested, but
accepted as it was stated strongly by Henrik).
4. For increasing cache store size, higher number of smaller disks yields
faster performance, compared to lower number of larger disks. This also
makes sense, as if you have to compare disk count / size performance, you
usually do that by disks available at any single point in time. So, if you
have an old cache with 4 IDE HDDs, and was considering to upgrade to SATA,
it would be better to buy 4 SATA drives rather than 2 larger SATA drives.
5. With cache size increases, it is important to have matching memory (RAM)
as well, as you need around 10 / 14 MB (32 / 64 bit) of RAM space for every
1GB of cache store. So, even if you have one single 1 TB HDD, with a 700GB
(assuming recommended 70% of disk space usage), you'll need 10GB for squid
to hold the index in memory. the Cache_Mem setting that you put in the
squid.conf is ON TOP of this 10GB, plus some memory for OS, and disk
buffers.
6. It is always best to have COSS plus AUFS / DISKD, as COSS is far
superior in handling smaller file sizes (< 128kB), and AUFS / DISKD is
superior than UFS in disk access.
If the gurus have any suggestions for changes / additions on this, it would
be very helpful.
Regards
HASSAN
----- Original Message -----
From: "Amos Jeffries" <squid3@xxxxxxxxxxxxx>
To: "Graham Dixon" <grahamdixon@xxxxxxxxxx>
Cc: <squid-users@xxxxxxxxxxxxxxx>
Sent: Monday, April 13, 2009 07:12
Subject: Re: multiple disks for cache storage
Graham Dixon wrote:
Gd morning all,
I have noticed in some (at least one) recent postings with description
of a system which included only one large disk media.
Some time ago when I first explored the pleasures of building my own
proxy I learnt that better performance could be obtained from the
technology of the time by building the cache storage on a disk system
seperate from the OS, and logs, and built with multiple small disks.
With advances in disk technology does such a concept still apply ?
Or do larger disk caches, higher access rates and other improvements
mean that such tricks to reduce average seek times for cache reads are
less important on busy machines.
cheers
Graham
AFAIK, the many small disks model still provides faster disk times than
the single large media.
The purchasing trend though seems to be towards fewer, bigger or cheaper
media. I've no idea if the newer disk improvements outperform multiple
older disks though. So the performance loss may not be as bad as it seems.
Amos
--
Please be using
Current Stable Squid 2.7.STABLE6 or 3.0.STABLE14
Current Beta Squid 3.1.0.7
