[pve-devel] backup ceph high iops and slow

[Alexandre DERUMIER]

about ceph new read-ahead feature :

https://github.com/ceph/ceph/commit/a9f302da08ab96128b28d85e2f566ad0f2ba2f30

+
+
+Read-ahead Settings
+=======================
+
+.. versionadded:: 0.86
+
+RBD supports read-ahead/prefetching to optimize small, sequential reads.
+This should normally be handled by the guest OS in the case of a VM,
+but boot loaders may not issue efficient reads.
+Read-ahead is automatically disabled if caching is disabled.
+
+
+``rbd readahead trigger requests``
+
+:Description: Number of sequential read requests necessary to trigger read-ahead.
+:Type: Integer
+:Required: No
+:Default: ``10``
+
+
+``rbd readahead max bytes``
+
+:Description: Maximum size of a read-ahead request.  If zero, read-ahead is disabled.
+:Type: 64-bit Integer
+:Required: No
+:Default: ``512 KiB``
+
+
+``rbd readahead disable after bytes``
+
+:Description: After this many bytes have been read from an RBD image, read-ahead is disabled for that image until it is closed.  This allows the guest OS to take over read-ahead once it is booted.  If zero, read-ahead stays enabled.
+:Type: 64-bit Integer
+:Required: No
+:Default: ``50 MiB``




So, It's important to setup : 

rbd readahead disable after bytes=0  for proxmox backups





----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre DERUMIER" <aderumier at odiso.com> 
Cc: pve-devel at pve.proxmox.com, "VELARTIS Philipp Dürhammer" <p.duerhammer at velartis.at>, "Dmitry Petuhov" <mityapetuhov at gmail.com> 
Envoyé: Samedi 18 Octobre 2014 09:47:08 
Objet: RE: [pve-devel] backup ceph high iops and slow 

> >>We read 64K blocks, so 
> 
> Don't for for backup, but drive-mirror have a "granulary" option to change the 
> block size: 
> 
> # @granularity: #optional granularity of the dirty bitmap, default is 64K. 
> # Must be a power of 2 between 512 and 64M. 

Although it would be much easier it read-ahead solve the problem ;-) 

Anybody have newest ceph with those read-ahead patches for testing?