Thanks Tyler, this is really useful.
Also, I noticed that you can specify multiple data file directories
located on different disks. Let's say if I have machine with 4 x 500GB
drives, what would be the difference between following 2 setups:
1. each drive mounted separately and has data file dirs on it (so 4x
data file dirs)
2. disks are in RAID0 and mounted as one drive with one data folder on it
In other words, does splitting data folder into smaller ones bring any
performance or stability advantages?
On 10/12/2010 00:03, Tyler Hobbs wrote:
Yes, that's correct, but I wouldn't push it too far. You'll become
much more sensitive to disk usage changes; in particular, rebalancing
your cluster will particularly difficult, and repair will also become
dangerous. Disk performance also tends to drop when a disk nears
capacity.
There's no recommended maximum size -- it all depends on your access
rates. Anywhere from 10 GB to 1TB is typical.
- Tyler
On Thu, Dec 9, 2010 at 5:52 PM, Rustam Aliyev <rus...@code.az
<mailto:rus...@code.az>> wrote:
That depends on your scenario. In the worst case of one big CF,
there's not much that can be easily done for the disk usage of
compaction and cleanup (which is essentially compaction).
If, instead, you have several column families and no single CF
makes up the majority of your data, you can push your disk usage
a bit higher.
Is there any formula to calculate this? Let's say I have 500GB in
single CF. So I need at least 500GB of free space for compaction.
If I partition this CF and split it into 10 proportional CFs each
50GB, does it mean that I will need only 50GB of free space?
Also, is there recommended maximum of data size per node?
Thanks.
A fundamental idea behind Cassandra's architecture is that disk
space is cheap (which, indeed, it is). If you are particularly
sensitive to this, Cassandra might not be the best solution to
your problem. Also keep in mind that Cassandra performs well
with average disks, so you don't need to spend a lot there.
Additionally, most people find that the replication protects
their data enough to allow them to use RAID 0 instead of 1, 10,
5, or 6.
- Tyler
On Thu, Dec 9, 2010 at 12:20 PM, Rustam Aliyev <rus...@code.az
<mailto:rus...@code.az>> wrote:
Is there any plans to improve this in future?
For big data clusters this could be very expensive. Based on
your comment, I will need 200TB of storage for 100TB of data
to keep Cassandra running.
--
Rustam.
On 09/12/2010 17:56, Tyler Hobbs wrote:
If you are on 0.6, repair is particularly dangerous with
respect to disk space usage. If your replica is
sufficiently out of sync, you can triple your disk usage
pretty easily. This has been improved in 0.7, so repairs
should use about half as much disk space, on average.
In general, yes, keep your nodes under 50% disk usage at all
times. Any of: compaction, cleanup, snapshotting, repair,
or bootstrapping (the latter two are improved in 0.7) can
double your disk usage temporarily.
You should plan to add more disk space or add nodes when you
get close to this limit. Once you go over 50%, it's more
difficult to add nodes, at least in 0.6.
- Tyler
On Thu, Dec 9, 2010 at 11:19 AM, Mark
<static.void....@gmail.com
<mailto:static.void....@gmail.com>> wrote:
I recently ran into a problem during a repair operation
where my nodes completely ran out of space and my whole
cluster was... well, clusterfucked.
I want to make sure how to prevent this problem in the
future.
Should I make sure that at all times every node is under
50% of its disk space? Are there any normal day-to-day
operations that would cause the any one node to double
in size that I should be aware of? If on or more nodes
to surpass the 50% mark, what should I plan to do?
Thanks for any advice
