On Mon, 23 May 2011, John R Pierce wrote: > To: centos at centos.org > From: John R Pierce <pierce at hogranch.com> > Subject: Re: [CentOS] SSD for Centos SWAP /tmp & /var/ partition > > On 05/23/11 9:54 AM, Gordon Messmer wrote: >> On 05/23/2011 07:23 AM, Michael Schumacher wrote: >>> As far as I understand, SSD are fast at reading and slow at writing. >> A good SSD will be substantially faster at writes than a disk drive, as >> well. Because there's no head seeking around a platter, latency is >> vastly better, which provides a massive performance advantage in many >> (if not most) use patterns. > > yes,butt.... SSD has to erase and write a LARGE block all at once, so > they don't do so well with the sorts of 8k random writes that write > intensive applications like relational databases commonly perform. To > write a single 8K block would require reading the whole flash block > (something like 64k or 256k), flash erasing that block, then rewriting > the whole thing. This would be painfully slow. So, what the drives > do instead is remap blocks rather randomly onto 'new' space, caching > them in drive-local buffer memory, then flashing whole blocks at once. > once the new space is used up, performance tends to degrade as they have > to scavenge scattered free blocks. Would a defrag program work on a SSD? Keith ----------------------------------------------------------------- Websites: http://www.karsites.net http://www.php-debuggers.net http://www.raised-from-the-dead.org.uk All email addresses are challenge-response protected with TMDA [http://tmda.net] -----------------------------------------------------------------