Tomasz Chmielewski wrote:
>>
>> with 8GB of ram, I would give a rough estimate that you can have up to
>> 500,000,000 files in flight at one time as far as ram is concerned!
>> that includes ALL hosts that would be backed up simultaniously. I doubt
>> RAM will be an issue for you. Probably hard disk speed will be the big
>> hurdle here. You have some pretty limited options here because you will
>> spend BIG BIG money getting a very fast RAID5/6 hardware array while
>> regular desktop drives will perform pretty poorly with a software
>> RAID5/6 because having the CPU do the checksums adds a lot of latency
>> with = poor write speed for large numbers of small files aka hard links
>> and directories aka 90% of what backuppc does.
>
> Err, no.
> CPU load because of RAID5/6 computations on today hardware is marginal.
> RAID5/6 have a performance penalty when compared to other RAID level
> because every single write (or, write IO operation) requires four disk
> IOs on two drives (two reads, and two writes), possibly harming other IO
> operations.
The seek time for these may be the real killer since you drag the parity
drive's head along for the ride.
>> just take Les' advice, split up the backup job among a few servers
>> instead of one BIG one.
>
> I guess he meant splitting one big backup job into several smaller
> (i.e., instead of backing up 1x350 GB, backup 7x50 GB, all that to one
> BackupPC server) - it is always a good idea for large backups.
That's mostly to help with rsync and it's need to transfer the entire
directory for a run before starting. At some other point you'll run
into a bottleneck from disk activity - which you probably can't fix
cheaply other than by moving some backups to a different server. You'll
know because sar will be showing most of the time in iowait during the
busy interval.
--
Les Mikesell
[EMAIL PROTECTED]
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